This study analyses the relative age effect (RAE) in basketball athletes, considering the categories (U13, U15, U17, and U19), sex, number of games and average points. The participants were 1,455 Brazilian athletes aged between 9 and 19 who participated in the Santa Catarina State Basketball Championship in the 2018 season. To test the RAE, the Chi-square test (χ2) was performed to compare the observed distribution and expected birth quartiles. To verify the differences between the birth quartiles concerning the average of points and the number of games, One-Way ANOVA with post hoc Bonferroni was applied. The effect size was verified using Eta². Odds Ratios and confidence intervals were calculated for all birth quartiles. In conclusion, it was found that, in the general sample of players participating in the Santa Catarina State Basketball Championship, there was an over-representation of players born in the first two quarters of the year in most of the categories analysed. However, significant dif- ferences were found in the number of games and average points only in male players in the U13 category. These results confirm that the player selection process is negatively biased towards boys born at the end of the year in the U13 category.