To examine the inยฏuence of prior knowledge on children's immediate and delayed recall of the details of a physical examination, 4-and 6-year-olds received a specially constructed check-up that included some typical, expected medical features (e.g. listening to the heart), while omitting others, and incorporated several atypical, unexpected procedures (e.g. measuring head circumference). Using a combination of open-ended and more speciยฎc probes, the children were assessed for their recall of expected and unexpected features that had been included in or omitted from the examination. Expectation based on prior knowledge aected three aspects of performance. First, correct recall of typical features that had been experienced exceeded that of unexpected features. Second, after a 12-week delay, spontaneous incorrect recall of expected-but-omitted features was considerable, with 42% of 4-year-olds and 72% of 6-year-olds making at least one intrusion, and essentially zero for atypical procedures that were unexpected and omitted. Third, when questioned directly about medical procedures not included in the examination, correct denials were high for atypical features, but at chance levels for those that were expected. The positive and negative inยฏuences of knowledge raise questions about children's abilities to dierentiate clearly between experience and expectation and have implications for understanding their testimony.