Herpes zoster has been associated with immune suppression, as has an increased risk of cancer. To determine whether patients with herpes zoster are at increased risk for subsequent cancer, we followed 590 residents of Rochester, Minnesota, for 9389 person-years after the diagnosis of herpes zoster. Subsequent relative cancer risks, overall and by specific site, were determined for the entire cohort and selected subgroups. In addition, relative risks of cancer during various intervals after the diagnosis of herpes zoster were determined. The overall relative risk was 1.1 (95 per cent confidence interval, 0.9 to 1.3). Relative risks of specific cancer sites were not different from unity except for those for colon and bladder tumors in women, both of which were slightly elevated. Patients with disseminated, recurrent, or gangrenous zoster, with postherpetic neuralgia, and with ophthalmic zoster wee not at elevated risk for subsequent cancer. These findings do not support the investigation of patients for occult cancer at the time of diagnosis of herpes zoster or enhanced surveillance for cancer after such a diagnosis.