The excess of NHL associated with HIV infection is well established. Clinically, HIV associated NHL is characterized by histological evidence of a high grade of malignancy, B cell origin, extensive extranodal involvement (most notably of the CNS) and poor prognosis. High grade B cell lymphoma or primary brain lymphoma in HIV infected individuals is considered diagnostic of AIDS by the Centers for Disease Control. The incidence of NHL among individuals with AIDS varies by subtype of lymphoma, age, sex, race and risk group. Younger individuals, males, whites and haemophiliacs are at higher risk than other groups. The incidence of HIV associated NHL is increasing. Because of the paucity of data on risk factors for this malignancy, the current possibilities for risk modification are limited to the prevention of HIV infection.