The aim of this study was to analyses the relative age effect in Brazilian basketball over a 15-year period by investigating possible intervening variables. 10,856 records of athletes from youth selection championships U15, U17, U22 and the professional league from 2004 to 2018 were analysed. The birth date, height, game position, geographic region, and team performance were analysed. We observed that the relative age effect is present from the U15 to the high-performance level. It was observed that relative age effect differs depending on region and game position. To conclude the RAE is an evident phenomenon in Brazilian basketball from the U15 up to the professional league. It varies according to the geographic region of the team and the player position. This trend has perpetuated over the years.