Context: The Zambian Ministry of Health has scaled-up human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) care and treatment services at primary care clinics in Lusaka, using predominately nonphysician clinicians. Objective: To report on the feasibility and early outcomes of the program. Design, Setting, and Patients: Open cohort evaluation of antiretroviral-naive adults treated at 18 primary care facilities between April 26, 2004, and November 5, 2005. Data were entered in real time into an electronic patient tracking system. Intervention: Those meeting criteria for antiretroviral therapy (ART) received drugs according to Zambian national guidelines. Main Outcome Measures: Survival, regimen failure rates, and CD4 cell response. Results: We enrolled 21 755 adults into HIV care, and 16 198 (75%) started ART. Among those starting ART, 9864 (61%) were women. Of 15 866 patients with documented World Health Organization (WHO) staging, 11 573 (73%) were stage III or IV, and the mean (SD) entry CD4 cell count among the 15 336 patients with a baseline result was 143/μL (123/μL). Of 1142 patients receiving ART who died, 1120 had a reliable date of death. Of these patients, 792 (71%) died within 90 days of starting therapy (early mortality rate: 26 per 100 patient-years), and 328 (29%) died after 90 days (post-90-day mortality rate: 5.0 per 100 patient-years). In multivariable analysis, mortality was strongly associated with CD4 cell count between 50/μL and 199/μL (adjusted hazard ratio [AHR], 1.4; 95% confidence interval [CI], 1.0-2.0), CD4 cell count less than 50/μL (AHR, 2.2; 95% CI, 1.5-3.1), WHO stage III disease (AHR, 1.8; 95% CI, 1.3-2.4), WHO stage IV disease (AHR, 2.9; 95% CI, 2.0-4.3), low body mass index (<16; AHR,2.4; 95% CI, 1.8-3.2), severe anemia (<8.0 g/dL; AHR, 3.1; 95% CI, 2.3-4.0), and poor adherence to therapy (AHR, 2.9; 95% CI, 2.2-3.9). Of 11 714 patients at risk, 861 failed therapy by clinical criteria (rate, 13 per 100 patient-years). The mean (SD) CD4 cell count increase was 175/μL (174/μL) in 1361 of 1519 patients (90%) receiving treatment long enough to have a 12-month repeat. Conclusion: Massive scale-up of HIV and AIDS treatment services with good clinical outcomes is feasible in primary care settings in sub-Saharan Africa. Most mortality occurs early, suggesting that earlier diagnosis and treatment may improve outcomes. ©2006 American Medical Association. All rights reserved.