PURPOSE: To define clinical outcome after definitive chemoradiotherapy (CRT) of anal carcinoma in HIV-infected patients treated with highly active antiretroviral therapy (HAART). PATIENTS AND METHODS: A multicentric cohort comparison of 40 HIV-positive patients with HAART and 81 HIV-negative patients treated with radiotherapy (RT) or CRT was retrospectively performed. Local disease control (LC), relapse-free survival (RFS), overall survival (OS), cancer-specific survival (CSS), toxicity, and prognostic factors were investigated. RESULTS: HIV-positive patients were younger (mean age, 48 v 62 years; P <.0005), predominantly male (93% v 25%; P <.0005), and with early-stage (P =.06) and large-cell histology (90% v 67%; P =.005) disease. RT or CRT resulted in complete response in 92% (HIV positive) and 96% (HIV negative) of cases. Five-year OS was 61% (95% CI, 44% to 78%) in HIV-positive and 65% (95% CI, 53% to 77%) in HIV-negative patients (median follow-up, 36 months). Five-year LC was 38% (95% CI, 5% to 71%) in HIV-positive and 87% (95% CI, 79% to 95%) in HIV-negative patients (P =.008) compromising CSS and sphincter preservation. Grade 3/4 acute skin (35% v 17% [HIV negative]; P =.04) and hematologic (33% v 12% [HIV negative]; P =.08) toxicity together approximated 50% in HIV-positive patients. RFS in HIV-positive patients was associated with RT dose (P =.08) and severe acute skin toxicity (P =.04). CONCLUSION: Long-term LC and acute toxicity represent major clinical challenges in HIV-positive patients with anal carcinoma. Even if fluoropyrimidine-based CRT is feasible and may result in similar response rates and OS as in HIV-negative patients, improved treatment strategies with better long-term outcome are warranted.