The objective of this study was to elucidate the mechanisms of an ischemic stroke in a human immunodeficiency virus, type 1 (HIV)-infected population. Several clinical and autopsy studies have suggested an increased incidence of strokes in HIV-infected persons. These studies have been performed on diverse populations with numerous confounds for strokes, including, drug abuse and coexistent opportunistic infection. Because of these confounding factors, it has been difficult to assess whether a unique stroke propensity exists among HIV-infected persons. A retrospective case-controlled study was carried out of patients registered in the Durban Stroke Data Bank (DSDB) (n=1298) located in KwaZulu Natal province of South Africa. Sixteen per cent of all strokes in young (<50 year old) black Africans living in KwaZulu Natal province on the east coast of South Africa reported to the DSDB occurred in association with HIV infection. This HIV-infected population was free of drug abuse and relatively devoid of opportunistic infections. The incidence rate of HIV in this stroke population paralleled that of the young black population at large, suggesting no significant overall increased rate of stroke in association with HIV. However, when compared to strokes occurring in an age- and sex-matched, HIV-seronegative control population, the cryptogenic stroke was more common in the HIV-infected population. Although the incidence of rate of stroke appeared to be no higher among HIV-infected young black Africans in the KwaZulu province than among HIV-seronegative controls, the increased incidence of a large vessel cryptogenic stroke in the former suggests the presence of a co-existent prothromobotic state.