Associations between reciprocal and complementary sibling interactions, sibling relationship quality, and children's socio-emotional problem solving were examined in 40 grade 5-6 children (M age = 11.5 years) from middle class, Caucasian, Canadian families using a multi-method approach (i.e. interviews, self-report questionnaires, daily diary checklist, narrative task). Findings demonstrated that reciprocal sibling interactions were positively associated with warmth, mutual esteem, happy daily exchanges, and negatively related to rivalry and dominance, whereas complementary interactions were positively related to upsetting daily exchanges. Further, reciprocal and complementary interactions differed significantly in relation to several relationship qualities, with reciprocal interactions emerging as a significantly stronger correlate of happy exchanges. Only reciprocal interactions were positively correlated with socio-emotional problem solving. Finally, birth order moderated the negative association of reciprocal interactions with rivalry and dominance and the positive association with socio-emotional problem solving. In each case, the effect was stronger for younger members of the sibling dyad. Findings are discussed in light of recent theory on the sibling relationship and children's development. (Contains 5 tables and 2 notes.)