Toxoplasmic encephalitis is a very common opportunistic infection in patients with AIDS (occurring in 5 to 15% of cases). It is the most frequent CNS manifestation in patients with previousToxoplasmainfection, as determined by the presence of specific antibodies.A diagnosis of toxoplasmic encephalitis should be suspected in patients who present with clinical symptoms such as fever, headaches or any neurological abnormalities associated with the presence of intracerebral abscess on computerised tomography scans and/or magnetic resonance imaging. Early diagnosis leading to early treatment is the best prognostic factor for this treatable, but severe, disease.The diagnosis is assessed by the response to therapy with a combination of pyrimethamine (50 mg/day) and sulfadiazine (4 g/day). which should lead to improvement within 5 to 10 days. The duration of acute therapy should be 3 to 6 weeks. A combination of pyrimethamine plus clindamycin is second-line therapy in patients who are intolerant of pyrimethamine and sulfadiazine (30 to 50% of cases). Maintenance therapy should be life-long to avoid relapses.The widespread use of primary prophylaxis with cotrimoxazole (trimethoprim-sulfamethoxazole) or a combination of dapsone plus pyrimethamine in patients who are positive for antitoxoplasmic antibodies and have a CD4+ lymphocyte count of less than 200 cells/μl (200 × 106cells/L) tends to decrease the incidence of toxoplasmic encephalitis. Physicians need to provide information to patients on the usefulness of primary prophylaxis to optimise compliance with treatments.