The adjustment and prosocial behaviour of 4-year-old children and their older siblings growing up in step-parent or single-parent families, or with two biological parents, was investigated within a longitudinal community study, the Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC). Mean differences in mothers' perception of adjustment were found for children in different family settings, with higher levels of problems and lower prosocial scores reported for those in single- and step-parent families than those in non-stepfamilies. Individual differences within each family setting were marked. With the exception of single parenthood, which remained a risk indicator for the 4-year-olds, the contribution of family type to differences in adjustment and prosocial behaviour largely disappeared when account was also taken of negativity in family relationships, maternal age, education level, depressive symptomatology, and history of previous live-in relationships, mothers' support networks, and the family's current financial and housing circumstances. Boys remained more at risk for adjustment difficulties than girls when this range of factors was taken into account. The limitations and implications of these findings on a community sample, a first step in a programme of research into family processes in children's adjustment, are discussed.