Objectives: Our aim was to investigate CD4+ cell recovery and adverse outcome after highly active antiretroviral therapy (HAART) under the Peruvian National Program for HIV. Methods: A prospective, observational study was conducted between May 2004 and September 2005. Data were collected from records of patients receiving HAART at a public hospital under the Peruvian National Program for HIV. Predictors of CD4+ cell count recovery and adverse outcome were analyzed by multiple regression. Results: Three hundred and twenty-six patients were included in the study. The mean increase in CD4+ cell count at six months was 114 cells/μl (95% confidence interval: 103-126). Patients with a lower CD4+ cell count at baseline and those starting HAART with a didanosine-based regimen had a higher increase in CD4+ cell count at six months. Patients starting HAART with a stavudine-based regimen had a lower increase in CD4+ cell count at six months. World Health Organization clinical stage IV at diagnosis of HIV infection, a low body weight at baseline, and starting HAART with a stavudine-based regimen were independently associated with an adverse outcome. Conclusions: The CD4+ cell response to HAART under the Peruvian National Program for HIV was comparable with reports from other countries. However, the fact that advanced clinical disease predicted adverse outcome emphasizes the need for earlier access to HAART. © 2007 International Society for Infectious Diseases.