The frequency of secondary malignant neoplasms occurring in patients treated for Hodgkin's disease at the Royal Marsden Hospital between 1963 and 1978 is reported and the literature is reviewed. 730 patients were reviewed and 583 patients permanently resident in the United Kingdom were included in the analysis. The frequency of leukaemia and solid tumors was determined from age- and sex-corrected data from the South Thames Cancer Registry. Thirty-seven malignancies were recorded in 36 patients including 9 leukaemias, 10 lung cancers, 6 skin cancers and 2 non-Hodgkin's lymphoma, all of which were observed in significant excess. When all remaining sites are combined, there was a slight excess but no one site is individually significant.