Human immunodeficiency virus (HIV)-infected patients are at increased risk for serious and recurrent bacterial infections. We hypothesized that the degree of immunosuppression may play an important role in outcomes for HIV-seropositive patients with infective endocarditis (IE). To test our hypothesis, we retrospectively reviewed 144 cases of IE in injection drug users. One hundred two patients with documented HIV status (45 HIV-seropositive patients and 57 HIV-seronegative patients) were included in the analysis. Eleven patients (6 HIV-seropositive patients and 5 HIV-seronegative patients) died in the hospital. Staphylococcus aureus, the most common etiologic pathogen causing IE in our series, was isolated from 32 HIV-seropositive patients (71.1%) and 32 HIV-seronegative patients (56.1%). A clear inverse correlation between mortality rate and CD4 cell count was demonstrated (r = -.625; P < .001). Both univariate and multivariate analyses supported the finding of significantly higher mortality rates among patients with CD4 cell counts of < 200/mm3 than among patients with CD4 cell counts of > 500/mm3 (OR, 14.7; 95% CI, 2.64-81.9).