This study examined the relationship between unselected first-year medical students' knowledge and attitudes about health or exercise and their personal physical fitness. The 131 subjects performed a maximal exercise test to determine physical fitness by measuring maximal oxygen consumption (VO2max), underwent hydrostatic weighing to assess body fat content (percent body fat), and completed a questionnaire to measure their knowledge and attitudes about health promotion/disease prevention and exercise. Many independent variables were significantly associated with VO2max in bivariate analyses, but only percent body fat, resting systolic blood pressure, and perceived barriers to health promotion/disease prevention and to exercise were significant predictors of VO2max (mL x kg-1 x min-1) in the multivariate analyses. The absolute VO2max (L x min-1) can be predicted from percent body fat, weight, and perceived barriers to health promotion/disease prevention. Freshmen medical students' attitudes toward health promotion/disease prevention and exercise constitute one of three strong predictors of physical fitness levels and should be determined, along with percent body fat and resting systolic blood pressure, when estimating fitness levels in a medical student population.