Immunochemotherapy with cyclophosphamide, adriamycin, vincristine, prednisone and rituximab (R-CHOP) is the standard treatment in non-immunosuppressed patients with diffuse large B-cell lymphoma (DLBCL), but its adequacy has not been definitively established in patients with human immunodeficiency virus (HIV)-related lymphoma. This phase II trial aimed to evaluate the safety and efficacy of six cycles of R-CHOP in patients with HIV-related DLBCL and to determine whether response to highly active antiretroviral therapy (HAART) had prognostic impact. Patients were eligible if they had performance status <3 and absence of active opportunistic infections. Eighty-one patients were enrolled, 57 in stages III or IV, International Prognostic Index (IPI) 0 or 1 (n = 26), 2 (n = 19), 3 (n = 20) and 4 or 5 (n = 16), and median CD4 lymphocyte count of 0·158 × 109/l. The main adverse events were neutropenia (48% of cycles) and infections (10% of cycles), which were fatal in seven patients. Complete response was achieved in 55 (69%) patients, with an estimated 3-year disease-free survival of 77% and 3-year overall survival of 56%. IPI score and virological response to HAART were the prognostic parameters for response and survival. In HIV-related DLBCL R-CHOP is feasible, safe and effective. The prognosis depends on lymphoma-related parameters and on the response to HAART.