OBJECTIVE: To explore the nature of paternal involvement in early child-rearing adopting a social developmental perspective, and estimate its effect on behavioural outcomes of children aged 9 and 11 years. SETTING: The data come from the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort recruited in the former county of Avon in the southwest of England. PARTICIPANTS: Out of the 14 701 children in this cohort who were alive at 1 year, 10 440 children were living with both parents at 8 months and were therefore eligible. Outcome data were available for 6898 children at 9 years and 6328 children at 11 years. MAIN EXPOSURE: Paternal involvement was measured using factor scores obtained through factor analysis of fathers’ responses on their participation in, understanding of, and feelings about their child’s early upbringing. OUTCOME: Behavioural problems were measured using the Strengths and Difficulties Questionnaire (SDQ) total difficulties score. RESULTS: 3 factors were identified in the factor analysis: Factor 1 described fathers’ emotional response to the child; factor 2 measured the frequency of fathers’ involvement in domestic and childcare activities; factor 3 characterised fathers’ feelings of security in their role as parent and partner. Children of fathers with high scores on factors 1 and 3 had 14% (OR 0.86, 95% CI 0.79 to 0.94, p=0.001) and 13% (OR 0.87, 95% CI 0.79 to 0.96, p=0.006), respectively, lower adjusted odds of behavioural problems at 9 years. Factors 1 and 3 were associated with comparable reduction in adjusted odds of behavioural problems at 11 years (OR 0.89, 95% CI 0.81 to 0.98, p=0.017 and OR 0.89, 95% CI 0.81 to 0.99, p=0.034, respectively). Factor 2 was not associated with the outcome. CONCLUSIONS: Psychological and emotional aspects of paternal involvement in children’s early upbringing, particularly how new fathers see themselves as parents and adjust to the role, rather than the quantity of direct involvement in childcare, is associated with positive behavioural outcomes in children.