Central-nervous-system toxoplasmosis developed in 7 of 269 patients with the acquired immunodeficiency syndrome reported to the New York City Health Department through July 1982. Focal neurologic abnormalities, mass lesions on computed-tomographic brain scans, lymphocytic cerebrospinal fluid pleocytosis, and detectable IgG antibody to Toxoplasma gondii were common; but IgG titers of 1:1024 or more, IgM antibody to T. gondii, and positive open brain biopsies were uncommon. Serologic findings suggested that the disease resulted from recrudescent rather than primary infection. Four of five patients improved when treated with sulfonamides and pyrimethamine, but 2 had relapses. An aggressive diagnostic approach and sometimes even empiric therapy are warranted when central-nervous-system toxoplasmosis is suspected in a seropositive patient with the acquired immunodeficiency syndrome.