The phenotypic consequences of the p.Arg577Ter variant in the α-actinin-3 (ACTN3) gene are suggestive of a trade-off between performance traits for speed and endurance sports. Although there is a consistent association of the c.1729C allele (aka R allele) with strength/power traits, there is still a debate on whether the null allele (c.1729T allele; aka X allele) influences endurance performance. The present study aimed to test the association of the ACTN3 p.Arg577Ter variant with long-distance endurance athlete status, using previously published data with the Brazilian population. Genotypic data from 203 long-distance athletes and 1724 controls were analysed in a case-control approach. The frequency of the X allele was significantly higher in long-distance athletes than in the control group (51.5% vs. 41.4%; p=0.000095). The R/X and X/X genotypes were overrepresented in the athlete group. Individuals with the R/X genotype instead of the R/R genotype had a 1.6 increase in the odds of being a long-distance athlete (p=0.012), whereas individuals with the X/X genotype instead of the R/R genotype had a 2.2 increase in the odds of being a long-distance athlete (p=0.00017). The X allele, mainly the X/X genotype, was associated with long-distance athlete status in Brazilians.