Survival rates were analysed for a population-based series of over 15,000 childhood cancers registered in Great Britain during 1971-85. There were highly significant improvements (P less than 0.001 for trend) in survival for many major diagnostic groups. Between 1971-73 and 1983-85 the actuarial 5-year survival rates increased from 37% to 70% for acute lymphoblastic leukaemia, from 4% to 26% for acute non-lymphoblastic leukaemia, from 76% to 88% for Hodgkin's disease, from 22% to 70% for non-Hodgkin's lymphoma, from 61% to 72% for astrocytoma, from 24% to 42% for medulloblastoma, from 15% to 43% for neuroblastoma, from 58% to 79% for Wilms' tumour, from 17% to 54% for osteosarcoma, from 26% to 61% for rhabdomyosarcoma, from 59% to 94% for malignant testicular germ-cell tumours and from 43% to 77% for malignant ovarian germ-cell tumours. These increases in population-based survival rates reflect the substantial advances in treatment of a wide range of childhood cancers since 1970. The two principal diagnostic groups for which there was no evidence of any trend were retinoblastoma, which already had an excellent prognosis with a 5-year survival rate of over 85%, and Ewing's sarcoma, for which the survival rate remained below 45%.