The authors studied the influence of familial longevity on the prognosis in 98 patients with Hodgkin's disease (HD) followed for a long period of time. The survival of parents and grandparents to patients older than 50 years of age who died from progressive HD was significantly shorter than that of ancestors to survivors in the same age group. The excess death rate among relatives to the deceased patients was mainly caused by tuberculosis, which suggests a T-cell defect. The prognostic information achieved by analyzing duration of life of ancestors was superior to that given by the clinical stage. No association between familial longevity and prognosis was observed in young patients (less than or equal to 50 years of age). These findings are consistent with the hypothesis that HD in the elderly may be a separate clinical entity, and may also have important implications as to the understanding and treatment of HD in the elderly.