This study investigates emotional and behavioural problems in children of parents diagnosed with cancer and examines the relationship with demographic and illness-related variables. Furthermore, agreement and differences between informants regarding child's functioning were examined. Members of 186 families in which a parent had been diagnosed with cancer participated. More emotional problems were reported for latency-aged sons (ill parents) and adolescent daughters (ill parents; self-reports), whereas also better functioning was reported in adolescent children (spouses), compared to the norm group. Age and gender-effects were found: latency-aged sons were perceived as having more emotional problems than adolescent sons (ill parents); adolescent daughters as having more emotional and behavioural problems than adolescent sons (ill parents; self-reports). Results indicated a higher prevalence of problems when the father was ill than when the mother was (spouses and self-reports). The treatment intensity affected adolescent daughter's functioning (spouses), whereas adolescent son's functioning was affected by relapsed disease (self-reports). Adolescents and mothers perceived comparable levels of problems, but fathers perceived problems in children to be less prevalent. Findings suggest that adolescent daughters and latency-aged sons are at risk for emotional problems following the diagnosis of cancer in a parent. The perception of child's functioning and potential influencing variables varied according to informant. Copyright (c) 2005 John Wiley & Sons, Ltd.