We compared the incidence of imaginary companions and impersonated characters in 152 three- and four-year-old children (75 males and 77 females). Children and their parents were interviewed about role play in two sessions. Although there were no sex differences in verbal ability or fantasy predisposition, there was a significant difference in the form of children's imaginary characters: girls were more likely to create imaginary companions, whereas boys were more likely than girls to actively impersonate their characters. There were no significant sex differences in the competence ratings of imaginary companions or impersonated characters. These results suggest that it is important to examine the form and function of children's pretense to understand sex differences in fantasy play.