The purpose of this study was to determine whether former participants in weight-control programs would provide valid weight data by self-report in telephone interviews. Participants were 39 women and 107 men (aged 28 to 63 years) who were in year 4 or 5 post-treatment. These represented 95% of participants who had completed all annual clinic visits. Self-reported body weights obtained by telephone interview were validated against weight measured directly in a university clinic. Overall, self-reported weight was 5.9 lb (2.7 kg) (standard deviation = 7.0 lb) (2.9%) lower than the measured weight. Using regression analysis, the strongest predictor of measured weight was reported weight, for both men and women. The bias in self-report of weight seen here is of about the same magnitude and direction as that seen in population studies. We conclude that the use of self-reported weight is not adequate for the assessment of long-term weight-loss maintenance unless the magnitude of discrepancy is adjusted for.