BACKGROUND Non-Hodgkin's lymphomas (NHL) are primary neoplasms derived from lymphocytes, and Kaposi's sarcoma (SK) is a multicentric disease of viral etiology and is associated with HIV. OBJECTIVE To study the etiopathogenesis and clinical characteristics of NHL and KS, describing their mutual factors. METHODS This retrospective investigation was performed on 101 medical charts. The patients were studied according to their age, gender, and HIV-positivity, following the PRISMA guidelines. The characteristics of the tumors and comorbidities were analyzed according to their age and lymphatic metastasis. RESULTS The mean age of the patients ranged between 15-87 years for NHL and between 25-54 for KS, but the age of patients with NHL associated with HIV did not surpass 34 years. The ratio male: female was 1,8:1 for NHL, but only men presented KS. HIV-positivity was found in five patients with NHL and in 14 with KS. The stages of NHL were: I (21%), II (18,4%), III (26,3%), and IV (34,2%), but KS were found only at III (40%) and IV (60%) stages. The lymphatic metastases were positive in 62 patients NHL and in four with KS. HIV-positivity occurred in 60% of patients with NHL and in 50% with KS. CONCLUSIONS The HIV seropositivity was revealed for most of patients during the NHL and SK propaedeutic and none of them present clinical manifestations of AIDS. NHL associated with HIV was found only in young patients. NHL and KS patients have similar epidemiological, clinical, and therapeutic characteristics.