Male dispersal patterns were analyzed across a nine-year period in a population of ring-tailed lemurs (Lemur catta) on St. Catherines Island (SCI), USA, to evaluate two ultimate explanations for male dispersal: inbreeding avoidance and intrasexual mating competition. As part of this analysis, we also compared patterns of dispersal at this site with data from wild populations. Overall, we found that patterns of male intertroop movement on SCI are similar to the wild with respect to the frequency and seasonality of male transfer. In Madagascar, males move between groups every 3.1–3.5 years [Sussman, International Journal of Primatol 13:395–413, 1992; Koyama et al., Primates 43:291–314, 2002] as compared with every 3.2 years on SCI. The majority of transfers on SCI occurred during the birth season, as occurs at one site in Madagascar, Berenty [Budnitz & Dainis, Lemur biology. New York: Plenum Press, p 219–235, 1975; Jones, Folia Primatologica 40:145–160, 1983]. One difference is that males perform natal transfers 1–2 years earlier on SCI than in the wild, which may be related to food provisioning on SCI. Males never transferred back into their natal troops, which is remarkable given the small number of groups on SCI. Although this pattern of movement can indicate inbreeding avoidance by males, the fact that male troop tenure was in many cases long enough to overlap with the sexual maturation of potential daughters did not support the inbreeding avoidance hypothesis for male secondary dispersal. Instead, the intrasexual competition hypothesis was strongly supported, because males were significantly more likely to transfer into groups having fewer adult males and a more favorable sex ratio than their pretransfer groups. Males therefore appear to be bypassing groups in which they would experience a greater degree of intrasexual mating competition during the breeding season. Am. J. Primatol. 70:650–660, 2008. © 2008 Wiley-Liss, Inc.