1962-6. No case without histological confirmation has been included. The information required for the dead children was obtained from the hospital notes, while for most of the surviving children the general practitioners interviewed the mothers and loaned to us the relevant hospital letters. Consultants were asked to supply the necessary details for the remainder. On checking the records against the death certificates the inaccuracy of the latter was found to be about 8 %. Nineteen cases certified as Wilms's tumour had to be discarded-two-thirds because the necropsy findings did not confirm the death certificate diagnosis, and one-third on account of copying errors owing to the similarity of the words "neuroblastoma" and "nephroblastoma."