In 11 680 individuals (18-85 years) maximal oxygen consumption (VO2max) was estimated indirectly in a maximal cycle test using a prediction model developed in a young population (15-28 years). A subsample of 182 individuals (23-77 years) underwent 2 maximal cycle tests with VO2max estimated indirectly in both tests and measured directly in one test. Agreement between the direct measurement and the indirect estimate of VO2max and repeatability of the indirect estimates of VO2max were examined by Bland-Altman plots, limits of agreement (LOA) and coefficient of repeatability (CR). The indirect method (mean VO2max=3 132 ml · min(-1)) underestimated VO2max as compared to the direct method (mean VO2max=3 190 ml · min(-1)) in men (bias: 58 ml · min(-1) (95% LOA-450 and 565)) and overestimated VO2max in women (mean VO2max=2 328 vs. 2 258 ml · min(-1), bias: - 70 ml · min(-1) (95% LOA-468 and 328)). The mean difference between the 2 indirect estimates was non-significant (men: - 11.9 ml · min(-1), women: 18.3 ml · min(-1)) with a CR of 279 ml · min(-1) (8.9%) in men and 274 ml · min(-1) (11.7%) in women. The validity of the indirect method was good despite minor sex-specific bias. Owing to this bias we suggest a new prediction model of VO2max. The maximal cycle test was highly repeatable.