We hypothesized that girls with congenital adrenal hyperplasia (CAH), who experience higher than normal levels of androgens prenatally, would show masculinization of behaviors that show sex differences. Therefore, we examined rough-and-tumble play and sex of preferred playmates in 3-8-year-old children with CAH and in unaffected 3-8-year-old male and female relatives. The hypothesized sex differences in rough-and-tumble play were seen, with unaffected boys showing more rough-and-tumble play than unaffected girls. However, CAH girls were similar to unaffected girls. Additionally, CAH boys showed reduced rough-and-tumble play. In contrast, sex of preferred playmates showed the hypothesized pattern of results. There were sex differences, with unaffected boys preferring boys and unaffected girls preferring girls. In addition, the preferences of girls with CAH were masculinized compared to those of unaffected girls. Results are discussed in terms of possible influences of social, hormonal, and illness factors.