In the law of evidence, similar fact evidence (or the similar fact principle) establishes the conditions under which factual evidence of past misconduct of the accused can be admitted at trial for the purpose of inferring that the accused committed the misconduct at issue.

In Canada, the rule was established in R. v. Handy, 164 CCC (3d) 481, 2 SCR 908 (2002):

Evidence of prior bad acts by the accused is admissible if the prosecution satisfies the judge on a balance of probabilities that, in the context of the particular case, the probative value of the evidence in relation to a specific issue outweighs its potential prejudice and thereby justifies its inclusion.

Questions arise as to how the Court is to measure the elements of this rule:

i) What constitutes a prior act of misconduct?

ii) Why does the Court speak of evidence in relation to a 'specific issue'?

iii) How is probative value determined?

The 2001 trial of Roy Whiting may have influenced the decision to change the law in England and Wales (R v Handy continues to govern the law in Canada). These changes were brought into force by the 'Bad Character' provisions of the Criminal Justice Act 2003 (sections 98 to 113). Although preceding these changes, Rosemary West's 1995 trial was cited as an example where similar fact evidence was crucial to the prosecution case.