We followed by CT 19 AIDS patients with cerebral toxoplasmosis. Diagnosis of cerebral toxoplasmosis was assessed on radiological and clinical basis, including the therapeutic response. CT allowed to confirm brain lesions (40 lesions in 19 patients) and to follow the evolution with treatment. Analysis of the CT features of these brain lesions permits to define some characteristic findings, though not pathognomonic. These lesions share common characteristics with other granulomatous diseases or with brain abscesses. The most frequently observed features are: target lesions (74%) with contrast enhancement (95%), frequently multiple (53%), associated with a hypodense area of oedema (100%), and responsible for a mass effect (79%). Under treatment, we observed improvement in 89%, resulting either in complete disappearance of the lesions (16%), disappearance of one or more contrast enhancing (46%) or hypodense (6%) areas, or volumetric regression of the hypodensities (50%). We conclude that CT is a good first-step examination for the detection and follow-up of cerebral toxoplasmosis in AIDS patients. MRI, a method with a higher sensitivity but still less accessible, may be considered at the present time as a second-step examination for those patients with solitary lesions on CT, or for symptomatic patients with normal CT.