Zoster is an important clinical problem for human immunodeficiency virus type 1 (HIV)-infected patients. Risk factors for tester and trends in incidence in HIV-infected hemophiliacs and homosexual men (n = 1218) were examined. From 1984 to 1997, 174 tester cases were identified (average yearly incidence, 2.5%). Prior tester episodes were associated with increased risk for a subsequent episode (relative risk [RR], 4.30; 95% confidence interval [CI], 3.11-5.95), Among hemophiliacs, children and adolescents had the highest tester risk, and tester risk declined with age (RR, 0.80 per decade; 95% CI, 0.68-0.93), These findings suggest that HIV-infected persons do not produce or maintain adequate booster responses after varicella tester virus exposure. Zoster risk was relatively constant when CD4 cell counts >200 cells/mm(3) but increased steeply below this level. During the 14 years of follow-up, tester incidence declined 9% per year. This trend occurred despite decreasing CD4 cell counts and was unexplained by zidovudine or acyclovir use.