OBJECTIVE: To determine the association of clinical pharmacists with health outcomes and utilization measures among HIV-infected patients. METHODS: Observational study of 1571 HIV-infected patients prescribed their initial highly active antiretroviral therapy (HAART) regimen in clinics with and without a clinical pharmacist. Outcomes analyzed were changes in plasma HIV RNA level, CD4 T-cell counts, and service utilization (hospital days, emergency department visits, and office visits) over 24 months based on exposure to a clinical pharmacist. RESULTS: Patients exposed to a clinical pharmacist tended to be more likely to achieve an HIV RNA level <500 copies/mL at 12 months (adjusted odds ratio [OR] = 2.01, 95% confidence interval [CI]: 0.92 to 4.37). At 24 months, however, results depended on the provider panel size; the ORs for panel sizes < or =50 and >50 HIV-infected patients were 1.67 (95% CI: 0.60 to 4.62) and 0.97 (95% CI: 0.39 to 2.41), respectively. CD4 T-cell counts were modestly but nonsignificantly higher for the patients exposed to a clinical pharmacist. Utilization also depended on the provider panel size; pharmacist exposure was associated with 64% (95% CI: 30% to 108%) and 9% (95% CI: -11% to 33%) increases in total hospital days for panel sizes < or =50 and >50 HIV-infected patients, respectively. Pharmacist exposure was also associated with a 19% (95% CI: -13% to -24%) decrease in office visits for panel sizes < or =50 HIV-infected patients, with minimal effect for larger panel sizes. CONCLUSION: Clinical pharmacists seem to contribute to lower office visit rates in antiretroviral-naive patients initiating HAART.