The use of performance-based examinations consisting of standardized-patient (SP) cases has increased greatly in recent years. These examinations are typically long and thus require the presentation of the same SP cases to several consecutive examinee groups. Consequently, concerns have arisen about the potential for violations of test security whereby students who were tested early in the examination period pass on information to students tested later. These concerns are addressed using data from the SP-based examinations administered to five classes (1986-1990) of senior medical students at Southern Illinois University School of Medicine. Because of the length of the examinations, each class was randomly divided into five groups and the examination was administered to one group at a time, requiring three days of testing time per group and three weeks of testing time per class. The results showed no consistent, systematic changes in case means across the five groups tested at different times throughout the examination period, and thus provide no evidence of serious, widespread violations of test security.