The rate of occurrence of herpes zoster (HZ) was analyzed by the life table method in 108 Hodgkin's disease (HD) patients, diagnosed and treated during the years 1969 to 1976. Three groups, divided according to the degree of severity of the disease, were compared. The cumulative rate of occurrence of HZ at the end of the third year after diagnosis was higher in the group with intermediately extensive disease than in that with the most extensive disease (35 vs. 23%), but the difference was not significant. At the end of the fifth year, the rate was almost identical in both groups (35.3 and 35.6%, respectively). The group with the least severe form of HD had a very low HZ rate (2.2%), which was significantly different from the other two groups and close to the rate reported for normal populations. The five-year mortality rate was 0.0, 20.3 and 40.6%, respectively, in the three groups. These findings were interpreted to mean that in more advanced stages of HD, therapy and not the severity of the disease is the main factor determining the incidence of HZ. Extended field irradiation followed by a few courses of combined chemotherapy appear to have an effect similar to that of prolonged chemotherapy.