Cerebral toxoplasmosis is one of the most common opportunistic infections among HIV-infected patients in France. The significant decline—estimated at 42%—in the incidence of toxoplasmosis between 1989 and 1993 is undoubtedly linked to the widespread use of prophylaxis. To better understand the circumstances surrounding the occurrence of cerebral toxoplasmosis in these patients, a prospective study was conducted in 1995 at the Centers for Information and Care on Human Immunodeficiency (C.I.S.H.), which bring together high-volume HIV care services in France. (R.A.).