Clitoromegaly in the neonatal period is an important morphologic sign that can be useful for sexual determination in aberrant cases. In rhesus monkeys, differentiation of the external genitalia occurs early during gestation (at 55 to 60 d) and is complete by approximately 80 d. Most of the critical steps in genital differentiation in primates occur prenatally. We sought to determine clitoral size in normal rhesus monkeys (Macaca mulatta) and possible effects of age and inheritance. Clitoral length was highly variable and had no relationship to fertility. Statistical evaluation revealed no association in the distribution of daughters with and without clitoris between mothers with and without clitoris. However, even when mated with several female monkeys, some male macaques produced primarily daughters without clitoris.