Time trends in mortality from Hodgkin's disease have been studied in Great Britain for the 70-year period, 1911-1980, and incidence in Scotland since 1959. In both Scotland and England and Wales, in each sex, mortality from Hodgkin's disease rose steadily from 1911 until 1970 and thereafter dropped substantially; the greatest fall was apparent in Scottish males. While mortality rates continue to decline in Scotland the incidence has remained fairly constant over the last 25 years suggesting a major change in prognosis for this disease. The introduction of effective chemotherapy and improved techniques of radiotherapy appear to have improved prognosis sufficiently, and to have been made adequately widely available, as to influence overall mortality rates at a national level as well as at the level of the clinical trial. No such improvement in prognosis, however, explains the declines observed in mortality rates among children of each sex in both areas which have taken place since the 1930s. In view of the current knowledge of the aetiology of Hodgkin's disease this fall may have been brought about by changes in socioeconomic factors.