California Evidence Code 1108: Prior Sex Offenses and Section 352

California Evidence Code section 1108 allows the prosecution to introduce evidence that a defendant committed other sexual offenses to show a propensity to commit the sexual offense currently charged.¹ That is a sharp break from the usual rule in California courts, which forbids using a person’s past conduct to argue they acted the same way again. The exception is powerful, but it is not automatic: the trial judge still has to admit the evidence after weighing its value against its potential for unfair prejudice, and the prosecution has to give the defense advance notice.

Why Section 1108 Is an Exception

Under Evidence Code 1101, California generally bars the prosecution from using a defendant’s character or past acts to argue that the defendant acted consistently with that character during the charged crime. Section 1101 does permit prior-act evidence for narrower purposes such as motive, planning, intent, identity, or the absence of mistake, so long as the purpose is not to argue the defendant is the type of person who commits crimes.²

Section 1108 flips that default for sexual offense prosecutions. It lets the prosecution argue exactly what section 1101 normally forbids: that the defendant’s past sexual conduct reveals a pattern, and the jury may use that pattern in deciding whether the defendant committed the charged sexual offense.¹ The statute does not make prior-offense evidence automatically admissible. It removes the section 1101 barrier, and then the evidence has to survive a separate balancing test under Evidence Code 352.

What Counts as a Sexual Offense

Section 1108 defines “sexual offense” broadly. It covers crimes under California or federal law involving any of the following:¹

Specific Penal Code violations, including rape, lewd acts with a child, unlawful sexual penetration, sexual battery, annoying or molesting a child, human trafficking for sexual purposes, and various child pornography offenses.
Nonconsensual sexual contact between the defendant’s body or an object and another person’s genitals or anus, or between the defendant’s genitals or anus and any part of another person’s body.
Sadistic sexual conduct, meaning deriving sexual gratification from inflicting death, injury, or pain on another person.
Attempts and conspiracies to commit any of the above.
Assault with intent to commit a sexual offense under Penal Code 220.

Because the definition reaches both state and federal offenses, a prior act from another jurisdiction can qualify if the underlying conduct fits one of these categories.

The Prior Offense Does Not Have to Be a Conviction

This is the part that catches most people off guard. Evidence admitted under section 1108 does not have to be tied to a prior conviction or even prior charges. The prosecution can present an uncharged act, an act that was investigated but never prosecuted, or an act the defendant was previously acquitted of. What matters is whether the jury in the current case believes, by a preponderance of the evidence, that the defendant committed the prior act.³

Preponderance of the evidence means “more likely than not.” That is a substantially lower bar than proof beyond a reasonable doubt, which the prosecution must still meet on the charged crime itself. If the jury does not find the prior act more likely than not, the instruction directs them to disregard the evidence entirely.³

The Section 352 Balancing Test

Even when a prior act qualifies as a sexual offense, the judge decides whether it reaches the jury. Evidence Code 352 gives the court discretion to exclude any evidence whose probative value is substantially outweighed by the risk of unfair prejudice, jury confusion, or wasted time.⁴ In section 1108 cases, this is where most contested pretrial battles happen.

The California Supreme Court laid out the factors trial judges should weigh in People v. Falsetta (1999):⁵

The nature and relevance of the prior offense to the charged crime.
Remoteness in time. A 25-year-old allegation carries less weight than a recent one, though no fixed cutoff exists.
Degree of certainty that the defendant actually committed the prior act. A prior conviction is more certain than an uncorroborated accusation.
Similarity between the prior act and the charged offense. Greater similarity increases probative value.
Prejudicial impact. If the prior act is far more inflammatory than the current charge, it risks the jury convicting out of disgust rather than proof.
The burden the evidence places on the defense in responding to a possibly old allegation.
Whether less prejudicial alternatives exist, such as admitting some prior offenses while excluding others or stripping out inflammatory details while preserving the relevant facts.

Falsetta also observed that prior offenses resulting in actual convictions tend to be less prejudicial than uncharged allegations, because juries are less tempted to convict the defendant simply to punish conduct that was never adjudicated.⁵ Trial judges have wide discretion in this analysis, and appellate courts rarely disturb a 352 ruling unless it was clearly unreasonable.

Notice Before Trial

The prosecution cannot spring prior-offense evidence on the defense at the last minute. Section 1108 requires disclosure of the evidence the prosecution intends to introduce, including witness statements or a summary of expected testimony.¹ Under Penal Code 1054.7, that disclosure must generally occur at least 30 days before trial.⁶

If the prosecution discovers the evidence within 30 days of trial, disclosure must be made immediately. The court can also allow later disclosure on a showing of good cause.⁶ Thirty days is not much time when the allegations may be years or decades old, so late-disclosure fights are a regular feature of pretrial motion practice in these cases.

What the Jury Is Told

When the court admits prior-offense evidence under section 1108, the jury receives a limiting instruction. CALCRIM 1191A covers uncharged prior offenses; CALCRIM 1191B covers prior offenses that were separately charged and proven. The instructions tell the jury three things:³

The jury may consider the prior-act evidence only if it first finds, by a preponderance of the evidence, that the defendant committed the prior act.
If the jury makes that finding, it may (but is not required to) infer that the defendant had a disposition to commit sexual offenses and was therefore more likely to have committed the charged crime.
The prior-act evidence alone is not enough for a conviction. The prosecution must still prove every element of the charged offense beyond a reasonable doubt.

Drawing that line in the deliberation room is not easy, which is why defense attorneys press hard to exclude the evidence at the 352 stage rather than trust a limiting instruction to contain it.

Is Section 1108 Constitutional

Section 1108 drew immediate due process challenges after it took effect in 1995. Defendants argued the law allowed convictions based on character rather than proof of the charged crime. The California Supreme Court rejected that argument in Falsetta, holding the statute constitutionally valid.⁵ The court pointed to the section 352 balancing test, the required jury instructions, and the pretrial notice requirement as safeguards that together prevent the kind of fundamentally unfair trial that would violate due process. Later challenges in state and federal courts have reached the same result.

Section 1108 Does Not Cover Domestic Violence

If your question involves a domestic violence charge rather than a sexual offense, a different statute applies. Evidence Code 1109 uses the same propensity-evidence framework for domestic violence cases. One difference matters: section 1109 imposes a 10-year presumption against admitting older acts, with the court retaining discretion to admit them in the interest of justice.⁷ Section 1108 contains no statutory time limit. A prior sexual offense from decades ago can still be admitted if it survives the section 352 balancing, though remoteness weighs against admission under the Falsetta factors.

1
California Legislative Information. California Evidence Code 1108 – Evidence of Commission of Another Sexual Offense
2
California Legislative Information. California Evidence Code 1101 – Evidence of Character
3
Justia. CALCRIM No. 1191A – Evidence of Uncharged Sex Offense
4
California Legislative Information. California Evidence Code 352 – Excluding Evidence
5
Justia Law. People v. Falsetta (1999)
6
California Legislative Information. California Penal Code 1054.7
7
California Legislative Information. California Evidence Code 1109 – Evidence of Domestic Violence