Ontogeny and sexual dimorphism have been important topics of investigation among researchers interested in the life history and ecology of non-human primates. It has been suggested that sex differences in the duration of growth are primarily, but not entirely, responsible for the sexual dimorphism observed in primate species with multimale–multifemale social structure, such as that seen in macaque monkeys (subfamily Cercopithecinae). Sexual dimorphism and growth was investigated in a wild population of booted macaques Macaca ochreata from Sulawesi, Indonesia. The results of our investigation suggest that the observed dimorphism in this population is primarily a product of greatly increased growth rates in dentally mature young adult males, in addition to prolonged male growth. This pattern of male growth may be an adaptive response to reduce the risk of adult male aggression before obligatory male emigration, and to facilitate competition for females soon after immigration into a new social group.