Late deaths after treatment for childhood cancer. An investigation of 749 deaths occurring among 4082 patients surviving at least five years after the diagnosis of childhood cancer in Britain before 1971 has been undertaken. Of the 738 with sufficient information the numbers of deaths attributable to the following causes were: recurrent tumour, 550 (74%), a second primary tumour, 61 (8%), a medical condition related to treatment of the tumour, 49 (7%), an traumatic death unrelated to the tumour or its treatment, 34 (5%), finally, any other cause unrelated to the tumour or its treatment, 44 (6%). Less than 10% of five year survivors of non-Hodgkin lymphomas, neuroblastoma, retinoblastoma, Wilms' tumour, or a soft tissue sarcoma died of recurrent tumour during the next 15 years, while more than 25% of five year survivors of Hodgkin's disease, ependymoma, medulloblastoma, and Ewing's tumour died of recurrent tumour during the corresponding period. Almost 50% of five year survivors of acute lymphoblastic leukaemia died of recurrent disease during the corresponding 15 years, a large proportion of deaths being due to central nervous system relapse in an era before central nervous system prophylaxis was routinely given. Comparison of the mortality observed with that expected from mortality rates in the general population indicated three times the expected number of deaths from non-neoplastic causes. Five times the expected number of deaths from cardiovascular causes were observed, these were predominantly myocardial infarction and cerebrovascular accidents. There was no evidence of an excess in the number of suicides observed, but there were three times the expected number of deaths from accidents observed after central nervous system tumours. 