We screened 192 patients infected with human immunodeficiency virus (HIV) to examine the relation between CD4+ lymphocyte counts and cytomegalovirus (CMV) viremia and the occurrence of CMV disease and subsequent duration of survival. When we stratified the viremic patients by CD4+ lymphocyte counts, the proportions were as follows: <50/mm3, 20 (25%) of 80 patients; 50-100/mm3, 2 (5.5%) of 36; 101-150/mm3, none of 14; and >150/mm3, 1 (1.5%) of 62. After a mean follow-up period of 8.5 months, 21 (11%) of 192 patients developed CMV disease. The probability of developing CMV disease at 6 months was 13% when the CD4+ lymphocyte count was <50/mm3, 3% when the CD4+ lymphocyte count was 50-100/mm3, and 0 when the CD4+ lymphocyte count was >100/mm3; this probability was 46% for viremic patients and 1% for nonviremic patients. In a multivariate analysis, CMV viremia was independently prognostic of CMV disease (relative risk, 22.03; 95% confidence interval, 6.49-78.97; P < .001), whereas a CD4+ lymphocyte count of <50/mm3 was not (P = .26). These results support the value of CMV viremia for predicting which HIV-infected patients are at risk of developing CMV disease and should therefore receive primary prophylaxis.