SUMMARYThe reactions of first‐born children to the birth of a sibling, as reported by their mothers, were studied in 40 families. Increased clinging, withdrawal and tearfulness were negatively related to positive interest in the baby, but other aspects of disturbed behaviour were not significantly associated with each other, or with positive interest. Differences in temperament, in the quality of the mother‐first‐born relationship, in age and in the mothers' State in thepost partumweeks were found to be associated with differences in the reaction of the first‐born c