Annual age cohort groupings promote relative age effects (RAEs), which often, inadvertently, create participation and attainment biases between relatively older and younger players within the same age cohort. In a globally evolving sport, women's rugby team selection practices may potentially bypass qualified players as a result of maturational differences.Our study examined the prevalence of RAEs in women's rugby union.Player data (age range = 4-21+ years) were gathered from the 2006 and 2010 Rugby World Cups (n = 498) and from Canadian (n = 1,497) and New Zealand (NZ; n = 13,899) developmental rugby leagues.Although no evidence of an RAE was found in the World Cup samples, chi-square analyses identified some typical and atypical patterns of RAEs at the developmental levels (w ≥ .3). Younger developmental groups displayed a typical RAE patterning with a greater representation of older players (Canadian 13-year-olds, w = .58; NZ 4-year-olds, w = .35), whereas older developmental groups displayed an atypical RAE patterning with a greater representation of younger players (Canadian 19-year-olds, w = .58; NZ 17-year-olds, w = .32). Further, a traditional RAE emerged in the Canadian 11- to 15-year-old age group, χ2(3) = 10.92, p < .05, w = .30.The lack of homogeneity of traditional RAEs across the sample questions the existence of a single, clear RAE in women's rugby. Some evidence of participation inequalities at the developmental levels suggests that further RAE research in more varied sociocultural contexts may be necessary.