We investigated concordance in social-emotional behavior and attachment of first- and secondborn siblings from 65 families. Both children were seen at 24 months in a problem-solving procedure and at 12 months in the Strange Situation. Maternal behavior at 24 months also was examined. Child behaviors at 24 months showed trends toward concordance across siblings. Maternal behavior was significantly stable across siblings and correlated significantly with child competence. In post-hoc analyses, the sample was split into 2 groups: maternal behavior stable (N = 36) and maternal behavior unstable. In the first group, cross-sibling correlations were significant and larger than for the whole sample; in the second group, cross-sibling correlations were low and nonsignificant. There also was significant concordance across siblings in attachment classification. These data suggest that it is essential to consider the care received by different children in investigating similarities in siblings' behavior.