Background: The ACTN3 R577X polymorphism has been associated with an elite athlete status. Several studies have determined that the R allele is connected with power-oriented athletic performance, whereas the nonfunctional XX genotype may give some beneficial effect for endurance performance. The main aim of the study was to determine the possible interaction between the ACTN3 R577X polymorphism and an endurance athlete status in a group of Polish rowers in comparison with sedentary individuals. Material/Methods: 121 male Polish rowers, members of academic sports clubs, and 115 unrelated volunteers were recruited for the study. Genotyping for the R577X variant was performed by PCR-RFLP. Results: The genotype distribution amongst the rowers (52.06% RR, 38.85% RX, 9.09% XX) was significantly different from that amongst sedentary individuals (RR-33.5%; RX- 49.60%; XX-17,35%; P = 0.024). A significant excess of the R allele was noted in the rowers (71.48%, P = 0.008) when comparing with the controls (60.0%). Conclusions: The obtained results show that the ACTN3 X allele and XX genotype are underrepresented in Polish rowers and they are not advantageous for the endurance-type athletes in the studied population. On the contrary, the R allele seems to be useful for a top-level rower. However, additional studies are needed to clarify this problem.