The purpose of this study was to provide three construct validity evidence for using fitness center attendance electronic records to objectively assess the frequency of leisure-time physical activity among adults. One hundred members of a fitness center (45 women and 55 men; aged 18 to 64 years) completed a self-report leisure-time physical activity questionnaire. The theory of planned behavior constructs (e.g., intention and perceived behavioral control), VO[subscript 2]max, and % BF were assessed. Fitness center attendance electronic records were expressed as the weekly mean number of mandatory check-in records retrieved from the fitness center's electronic database over a 12-week period prior to participant's physical fitness evaluation. A continuous (frequency) and categorical ("adherent" versus "non-adherent") scores were computed. Results indicated that perceived behavioral control was associated with fitness center attendance electronic records and mediated the fitness center attendance electronic records-intention relationship. Fitness center attendance electronic records were associated with VO[subscript 2]max and self-report leisure-time physical activity. Therefore, results provide three evidence of construct validity of using fitness center attendance electronic records scores to assess leisure-time physical activity behavior.