We retrospectively reviewed 414 episodes of pneumococcal bacteremia that occurred in adults from July 1986 through June 1987 (1986/1987) and from July 1996 through June 1997 (1996/1997) to monitor the incidence and clinical and laboratory characteristics and to assess the influence of human immunodeficiency virus (HIV) infection on any changes. The incidence increased from 26 per 100,000 persons in 1986/1987 to 36 per 100,000 persons in 1996/1997; the increase was most marked among patients who were aged 25-44 years (24 cases per 100,000 persons to 45 per cases 100,000 persons) and > or =65 years (43 cases per 100,000 persons to 50 cases per 100,000 persons). Of 161 patients who were tested for HIV in 1996/1997, 108 (67%) were HIV seropositive. Among the general population, the prevalence of other underlying diseases and smoking decreased from 45% and 67%, respectively, in 1986/1987 to 23% (P<.0001) and 35% (P<.0001) in 1996/1997. Strains of pneumococci that were not susceptible to penicillin were found in 4% patients in 1986/1987 and 12% in 1996/1997 (P=.005). This increase occurred exclusively among the HIV-infected patients (22% of the HIV-seropositive patients versus 4% of HIV-seronegative patients; P=.008), and there was a parallel increase for childhood serotypes (51% of HIV-seropositive patients versus 17% of HIV-seronegative patients; P<.0001).