Studies involving the administration of anti-androgens to spotted hyaenas during fetal development have raised questions concerning the precise contributions of steroids to phallic growth in these animals. If gonadal androgens promote postnatal penile growth in males, the following would be expected: (a) a period of accelerated growth accompanying achievement of puberty, and (b) a marked reduction in adult penile size and density of penile spines after gonadectomy. If a similar androgenic pubertal process stimulates clitoral growth in these highly 'masculinized' hyaenas, parallel observations in females would be expected; however, the role of oestrogens in accounting for female-typical clitoral development would also have to be considered. The results of the present study suggest a limited role, if any for androgenic stimulation of phallic growth. That is, penile growth was greater during the 10 month period preceding puberty, than during an 18-month period that included the traditional increase in pubertal androgens. In addition, pre-pubertal castration had minimal effects on penile length, diameter, or the presence of penile spines. In females, most clitoral growth also occurred before puberty, although pre-pubertal ovariectomy produced significant reductions in clitoral diameter and the elasticity of the urogenital meatus. These feminine characteristics which normally distinguish the female from the male phallus in this species, were partially restored by a brief period of oestrogen administration. Both sexes displayed erections many years after pre-pubertal castration. The results of the present study suggest that postnatal phallic growth is largely independent of gonadal steroids, with oestrogenic facilitation of female-typical clitoral characteristics in spotted hyaenas.