BACKGROUND: Adult survivors of childhood cancer have impaired psychosocial functioning, but not much is known about the causes. In this study we examined the role of relationships with parents as a possible mediating factor. METHOD: One hundred and two adult survivors (82% of those eligible, 35 female and 57 male) of childhood Acute Lymphoblastic Leukaemia and Wilms' Tumour, and 102 matched controls (74% of those eligible) aged 19-30 were interviewed. Interpersonal and social role functioning, and current relationships with each parent were assessed in standardised investigator-based interviews with subjects. RESULTS: Adult survivors were more likely than controls to have impaired close relationships (love relationships and friendships), and poorer day-to-day coping. Lower encouragement from fathers and greater involvement with mothers were each independently associated with impaired close relationships outside the family. This association was evident across the sample and in the cancer survivor group. It was much stronger in young adult females. Lower paternal encouragement was also associated with poor day-to-day coping, and this association was stronger in young men. There was, however, little evidence that quality of relationships with parents mediated the link between childhood cancer and adult psychosocial functioning. CONCLUSIONS: Within this cross-sectional design we could not determine the direction of influence, nor exclude third variable effects. However, the findings indicate that mothers and fathers have different roles in the transition to adult life, and understanding these may assist the development of interventions designed to improve adult psychosocial functioning.