Data analyzed for this project were from a cohort that had been under observation in the Aerobics Center Longitudinal Study. Baseline preventive medical examinations were given to 6,902 men and women during the interval from 1971-1982. Current physical activity and physical fitness levels (maximal exercise treadmill test) were assessed at baseline. Participants also completed a lifetime physical activity pattern questionnaire as part of a mail survey done in 1986. Self-reported physical activity from the 1986 questionnaire was used to categorize participants' physical activity levels for the years 1971-1985. These recalled levels of activity were compared to physical activity and physical fitness levels assessed during those same years at the baseline examinations (measure of truth). For example, participants who reported in the 1986 survey that they engaged in relatively high levels of physical activity in 1976 were expected to have recorded higher levels of physical fitness at the 1976 examination than participants who reported in 1986 that they were relatively sedentary in 1976. The study design permitted evaluation of how accurately participants recalled their physical activity up to 15 years in the past and allowed quantification of the errors investigators might expect from such assessments.