Objective The purpose of this study is to investigate psychiatric diagnoses given to children affected by parental cancer in psychiatric and somatic specialized health care settings. Methods The 1987 Finnish Birth Cohort data (n = 59 476) were followed up through national registers from birth of cohort members up to the end of 2008. The health‐related data of cohort members and their parents were obtained from the Care Register of Health Care provided by the National Institute of Health and Wellbeing. Results By the age of 21 years 7711 of the cohort members had used specialized psychiatric outpatient care and, of them, 549 (7.1%) were affected by parental cancer. Of affected offspring a mental disorder diagnosis was made in 424 (77.2%), while 125 (22.8%) children had not been given any specific mental disorder diagnosis. In females the likelihood for a mental disorder diagnosis assessed in outpatient care was significantly increased by up to 1.2 fold in cases of parental cancer. In males with a father having cancer, psychological development disorders were significantly increased whether assessed in outpatient (OR 1.5) or inpatient (OR1.9) settings. Conclusions The prevalence of psychiatric diagnoses in children with parental cancer does not seem to differ from those of children with parents without cancer. However, evidence was found that children affected by parental cancer are at increased risk for some specific psychiatric disorders. Quarter of affected offspring who were referred to specialized psychiatric outpatient care only received diagnoses related to use of health care services or crises or received no psychiatric diagnosis at all. Copyright © 2016 John Wiley & Sons, Ltd.