To assess the efficacy of pyrimethamine (Pyr) for primary prophylaxis of cerebral toxoplasmosis (CT) in HIV patients (pts), 554 pts were randomized in a double-blind, placebo-controlled trial (mean follow-up: 14 months). The intent-to-treat analysis found no significant difference in the incidence of ct at 1 year: 12% (Pyr) versus 13% (Pcb) nor in survival. Side-effects leading to stop the study drug were more frequent in Pyr group, especially cutaneous rashes: 8% (Pyr) versus 2% (Pcb).