We tested the peer-socialization/contextual-amplification explanation for the link between early female puberty and problem behaviour. We propose that in cultures with high tolerance for adolescent heterosexual involvement, early puberty should be linked with problem behaviour--not in other cultures. We compared girls in two cultures (Slovakia and Sweden) that differ in acceptance of adolescent girls' heterosexual involvement. Findings supported the hypothesis by showing that in Sweden, a culture that facilitates adolescent heterosexual involvement, early-maturing girls reported more problem behaviours than in Slovakia. The mediation link (heterosexual involvement as the mechanism linking early puberty with problem behaviour) was moderated by culture. The findings expand our understanding of the role of macro-cultural contexts in the developmental significance of female puberty. (Contains 3 tables and 3 figures.)