BACKGROUND AND OBJECTIVE: There are no previous studies on toxoplasmosis in HIV infected adults from Zaria, Nigeria. This study was undertaken in Zaria to determine the seroprevalence and risk factors of toxoplasmosis as well as the incidences of complications of toxoplasma infection in HIV infected patients and healthy HIV negative individuals. METHODS: A one year cross sectional study was carried out in Ahmadu Bello University Teaching Hospital, (ABUTH), Zaria in 2008. Eighty eight adult HIV infected patients and 90 HIV negative healthy adult controls were recruited consecutively. Patients and controls were matched for age and sex and were from similar environments in northern Nigeria. Toxoplasma infection was diagnosed serologically by serum positivity to IgM and or IgG anti-toxoplasma antibodies using an ELISA based assay. All patients were evaluated for features of toxoplasma encephalitis and chorioretinitis. Other clinical details, CD4 T cell counts and risk factors for toxoplasma infection were also documented. RESULTS: The seroprevalence of toxoplasma infection was 39.8% in HIV positive patients and 33.3% in HIV negative healthy controls (p>0.05). Toxoplasma seropositivity was not significantly associated with age, gender, type of meat ingested, ingestion of raw or undercooked meat and contact with cat in both patients and controls. Seventy percent of the toxoplasma seropositive patients were asymptomatic. Two patients (2.3%) were diagnosed with toxoplasma encephalitis and both cases had CD4 T cell counts below 20 cells/ul. No case of toxoplasma chorioretinitis was identified. CONCLUSIONS: This study’s findings show that Toxoplasma gondii is prevalent in the environment with both HIV patients and controls showing significant seropositivity. The predominant feature is asymptomatic and the immunosuppression induced by HIV leads to severe complications such as toxoplasma encephalitis in HIV infected ii patients in this study. This outcome justifies routine preventive education and screening for toxoplasmosis in all HIV infected patients in Nigeria