This study examined age and sex differences in dyadic and group interaction in a standardized setting. Seven classes of 4-year-old children and 6 classes of 6-year-old children participated. From these classes, 13 male playgroups and 13 female playgroups were formed. The playgroups were videotaped, and frequencies of dyadic and group interaction were tabulated. Results showed that boys and girls at both ages engaged in similar frequencies but different patterns of dyadic interaction. Only 6-year-old boys, however, interacted in groups. The discussion considers the etiology of these age and sex differences.