Thirty physicians in a university family medicine teaching practice were asked to estimate their rate of prescribing diazepam to six age/sex groupings of patients within their practice. Their actual prescribing rates as recorded by a computerized data collection system were not accurately perceived. After the physicians were informed of the gap between perceived and actual prescribing, significant changes in prescribing behavior occurred. Awareness of a perception-reality gap in primary care practice prescribing offers a method of continuing medical education that may significantly alter prescribing behavior in ways beneficial to patient care.