The investigation of the ability to attribute mental states to others and to see them as the basis for people's actions has been referred to as "theory of mind" (ToM) research. This study assessed ToM, or social understanding, in preadolescents and examined individual differences in the relations among social understanding, self-concept, and language competence. One hundred twenty-eight preadolescents (64 girls, 64 boys; mean age =11 years, 9 months) completed tasks concerning self-concept and vocabulary and participated in a story-telling interview that assessed social and self-understanding. There were positive associations between children's social understanding and (a) self-understanding, (b) selfperceptions of behavioral conduct, and (c) general vocabulary ability. Independent of vocabulary ability, girls scored higher than boys on both social and self-understanding tasks.