The aim of the present study was to assess the validity of different self-reported questions for measuring exercise behavior of 551 employees. Values of maximum oxygen intake, body mass index, muscular endurance, and a fitness profile, based on the individual results obtained from each of the three physiologic parameters, were used as validity criteria for the self-reported measures. The influence of fitness profile on the measures of exercise habits indicated that the fit employees reported a more active pattern of exercise behavior, participated in more strenuous physical activity, and expended a greater amount of energy in a typical week than the unfit employees. There was no gain obtained in explaining fitness categorization with a more elaborate method compared with a simple question in measuring exercise behavior. The results of the present study show that the suggested simple method (one question) for assessing exercise behavior of employees is valid and can be useful for nurses and company physicians when evaluating the baseline behavior of a group of employees to assess the impact of exercise promotion programs at the work site.