Hodgkin's disease incidence has an early peak in young adulthood. The US Navy maintains computerized career history and hospitalization information for one of the largest defined populations of young adults available for prospective studies. There were approximately 2.3 million person-years at risk in white male enlisted personnel involved in more than 80 occupations in the Navy from 1974-79. During this period 88 incident cases were identified. Navy age-adjusted incidence rates of Hodgkin's disease did not differ significantly from US population rates. There was a slight, but not significant, increased incidence with increasing length of Navy service. One occupation, machinists' mate, had about double the risk of Hodgkin's disease as the entire Navy (SIR = 2.3, p = 0.004) and the US population (SIR = 1.8, ns). Probable exposures of machinists' mates include: volatile solvents, metal dusts and, possibly, ionizing radiation. Further studies are needed, however, to clarify this association.