There have been relatively few epidemiological studies to verify the information obtained from study participants on the use of menopausal hormone replacement therapy. We conducted this study as part of a case-control study of diet, hormone use, and endometrial cancer in Toronto, Ontario, Canada, 1994–1998. We compared records from 653 subjects, 30–79 years of age, with reports from their physicians on ever/never use of hormone replacement therapy and duration, type, and dose of hormone replacement therapy. A total of 88% of the interview records were in agreement with physician reports for ever/never use of hormone replacement therapy. The overall kappa value for ever/never use agreement was 0.76 (range = 0.71–0.81), and the intraclass correlation coefficient was 0.64 (range = 0.57–0.70) for duration of hormone replacement therapy use, indicating good agreement; similar correlations were seen among cases and controls for overall use, as well as estrogen- or progestogen-alone use. Concordance for brand codes was observed for about 43% of the subjects. This study suggests that information obtained by interview in case-control studies provides a reasonable measure of ever use of hormone replacement therapy and duration of use. Interviews, however, do not represent a reliable source of information on brands and dosage of hormone replacement therapy preparations. (Epidemiology 1999;10:260–263)