The characteristics of 14 HIV-seropositive patients with NHL consecutively observed between 1984 and 1988 at our Institution are described. Patients belonged to a known population of 1242 HIV-seropositive individuals in whom the incidence of NHL was 1.13%, significantly higher than in age-matched controls (P less than .0001). Within this population, a previous diagnosis of ARC or AIDS, but not of LAS, was the only significant risk factor for the development of NHL (P less than .0001). According to the status of HIV infection at the time of NHL diagnosis, two groups of patients could be clearly identified with different clinicopathological features and prognosis. In fact, NHL developing in 7 patients previously affected by ARC or AIDS, presented as localized, extranodal disease, predominantly in the CNS; large cell histology, peripheral blood cytopenia, severe immunodeficiency and poor prognosis further distinguished this subgroup. Conversely, NHL developing in 7 patients with either asymptomatic HIV-seropositivity or LAS, more often presented as disseminated disease both in nodal and extranodal sites, with Burkitt's-type histology. Cytopenia was uncommon and immunodeficiency was significantly less severe. In this subgroup complete remission (CR) was achieved with aggressive treatment in 6 of 7 patients. No relapses occurred but two opportunistic infection-related deaths were observed. Four patients are alive 6-34 months after CR, two of whom show newly developed opportunistic infections.