Adopted children show more problem behaviors than nonadopted children. Given that internationally adopted individuals show earlier puberty than nonadopted individuals, and early puberty is associated with problem behaviors in nonadopted youth, we analyzed data from adopted domestic adoptees to determine whether problem behaviors could be explained by differences in pubertal timing. Relative to nonadopted controls (n = 153), domestically adopted girls (n = 121) had earlier menarche, earlier sexual initiation, and more conduct disorder symptoms. Age at menarche partially mediated the relation of adoptive status to sexual initiation, but not to conduct disorder symptoms. Extending findings from international adoptees, results show that domestic adoption is also linked to earlier puberty, and suggest early puberty as one mechanism linking adoption to problematic outcomes. (Contains 2 tables and 1 figure.)