In the interest of fairness, many sports impose age grades within youth sport, with the intention that children will be competing with others of a similar physical and cognitive development. The relative age effect (RAE) refers to the finding that individuals born relatively soon after the cut-off date tend to be over-represented at the higher levels of certain sports. The current study examined whether RAEs were present in 3726 professional rugby players registered for the 2014 season in the top eight ranked countries in the world. The results indicated that an RAE existed in both top tier and second tier competitions in the South African cohort, only in the second tier competition in the Australian and French cohorts, and only in the top tier competition in the New Zealand and English cohorts. No RAE was found within the Irish, Welsh or Scottish cohorts. These results suggest that the presence of an RAE is influenced by both nationality and playing level. The existence of an RAE in senior professional rugby suggests an underpinning problem at the youth level in selected countries.