Purpose Low functional capacity is associated with cardiovascular risk factors. Cardiopulmonary exercise test (CPET) is the gold standard evaluation to determine functional capacity through maximal oxygen uptake (VO 2 max) measurement. However, the high financial cost, the material and the time spent on this method difficult its use in a large number of clinicals. In this sense, it is possible to determine VO 2 max via the equivalence formulas. The aim of this study was to verify the agreement between indirect calculation of VO 2 max using American College of Sports Medicine (ACSM) equation and the directly measure of maximal oxygen uptake in metabolic syndrome (MetS) patients. Methods Sixty non‐diabetic and without medication patients with MetS (ATP‐III) were divided in 2 groups, according to gender: Male (n=32; 46±9 y; 31.2±3.0 kg/m 2 ); and Female (n=28; 49±9 y; 32.7±3.1 kg/m 2 ). VO 2 max was measured during CPET in a cycle ergometer with ramp protocol and estimated by ACSM’s equation [VO 2 = 7.0+ (1.8 x work rate)/body mass]. Results All patients included achieved respiratory exchange rate (RER=VCO 2 /VO 2 ) >1.10 at maximal exercise. In Male group, despite correlation between methods (R=0.78; P =0.0001), VO 2 max estimated by ACSM’s equation was higher than the VO 2 max of the direct measurement (28.7±3.1 vs. 26.9±6.0 ml/kg/min; P =0.049). Similarly, in Female group there was correlation (R=0.79; P =0.0001), however VO 2 max estimated by ACSM’s equation was higher than direct measured VO 2 max (20.3±3.3 vs. 18.8±3.3 ml/kg/min; P =0.0008). In both genders, Bland‐Altman plot analysis suggested a lack of agreement between predicted and direct VO 2 max. Conclusion In bout groups, Male and Female, the ACSM’s equation overestimates the VO 2 max. It seems that ACSM’s equation is not capable of accurately predicting VO 2 max in men and women with MetS.