Introduction: There is a need for simple and feasible methods for estimation of cardiorespiratory fitness (CRF) in large study populations, as existing methods for valid estimation of maximal oxygen consumption are generally time consuming and relatively expensive to administer. The Danish step test may be a feasible alternative for estimation of VO(2max.)Aim: To compare a simple fitness test, the Danish step test, to an indirect maximal test, the watt-max test, for estimation of VO(2max.)Methods: In the population-based Health2008 study, 2218 men and women aged 30-60 years were invited. Altogether, 795 eligible participants (response rate 35.8%) performed the watt max and the Danish step test. Correlation and agreement between the two VO(2max) test results was explored by Pearson's rho, Bland-Altman plots, Kappa(w), and gamma coefficients.Results: The correlation between VO(2max) (ml/kg/min) estimated by the two tests was moderate to high (men: r = 0.69, p <0.0001; women: r = 0.77, p <0.0001). The Danish step test slightly overestimated VO(2max )compared to the watt-max test, more so in women than in men. Agreement between the two tests when VO(2max) was classified in five levels was gamma = 0.77, Kappa(w )= 0.42 in women, and gamma = 0.64, Kappa(w )= 0.37 in men.Conclusion: The Danish step test is a safe and feasible alternative to the more time-consuming watt-max test as a method for estimation of VO(2max )in large adult population-based studies.