In 1970 the epidemiologic similarities between Hodgkin's disease and multiple sclerosis were first described, suggesting that a common agent or agents might be involved in their etiology. The hypothesis proposed at that time was that the agents followed the paralytic polio model: widespread infection with an agent of low pathogenicity at an early age, resulting in acquired immunity in later life. Lack of early infection results in the disease appearing in adulthood, with severe repercussions. This article extends the paralytic polio model to include testicular carcinoma, since the epidemiologic similarities between it and Hodgkin's disease are striking. Specifically, the authors compare age at clinical onset, histologic type, time trends, race, socioeconomic status, geographic variation, occupation, and familial aggregation. It is suggested that the possibility of common etiologies involved in the pathogenesis of these two cancers be tested further by epidemiologic, clinical, or laboratory studies.