The aim of the study was to investigate allele and genotype distributions of the muscle-specific creatine kinase gene (CKMM) A/G polymorphism in athletes (n = 384) and controls (n = 1116), and to find interrelation between genotypes and aerobic capacity in rowers (n = 85). Genotyping was performed by restriction fragment length polymorphism analysis. Aerobic capacity (maximal oxygen consumption (VO2(max)) and maximal power production capacity (W(max was determined using an incremental test to exhaustion by rower ergometer. The frequencies of CKMM A allele and AA genotype were significantly higher in endurance-oriented athletes (n = 176) than in controls (A allele: 78.7% vs. 65.4%; p < 0.0001; AA genotype: 59.7% vs. 44.2%; p = 0.0003). On the other hand, GG genotype was more prevalent in weightlifters (n = 74) in comparison with controls (31.1% vs. 13.4%; p = 0.0001). Furthermore, CKMM AA genotype was associated with high values of VO2(max) (AA - 58.98 (3.44) ml/kg/min, GA - 56.99 (4.36) ml/kg/min, GG - 52.87 (4.32) ml/kg/min, p = 0.0097). Thus, CKMM gene A/G polymorphism is associated with physical performance of athletes.