Self-report is often used to estimate health care utilization. However, the accuracy of such data is of paramount concern. The authors conducted a systematic review of 42 studies that evaluated the accuracy of self-report utilization data, where utilization was defined as a visit to a clinical provider or entity. They also present a broad conceptual model that identifies major issues to consider when collecting, analyzing, and reporting such data. The results show that self-report data are of variable accuracy. Factors that affect accuracy include (1) sample population and cognitive abilities, (2) recall time frame, (3) type of utilization, (4) utilization frequency, (5) questionnaire design, (6) mode of data collection, and (7) memory aids and probes.