The aim of the present pilot study was to compare the efficacy and safety of trimethoprim (TMP) and sulfamethoxazole (SMX) with those of the standard therapy pyrimethamine (P)-sulfadiazine (S) for the treatment of toxoplasmic encephalitis in patients with AIDS. This was a pilot, multicenter, randomized, and prospective study. Patients were randomly assigned to receive TMP (10 mg/kg of body weight/day) and SMX (50 mg/kg/day) or P (50 mg daily) and S (60 mg/kg/day) as acute therapy (for 4 weeks) and then as maintenance therapy for 3 months at half of the original dosage. Seventy-seven patients were enrolled and randomized to the study: 40 patients were treated with TMP-SMX and 37 were treated with P-S. There was no statistically significant difference in clinical efficacy during acute therapy. In contrast, patients randomized to TMP-SMX appeared more likely to achieve a complete radiologic response after acute therapy. Adverse reactions were significantly more frequent in patients treated with P-S, and skin rash was the most common adverse event noted in these patients. In conclusion, the results of the study suggest that TMP-SMX appears to be a valuable alternative to P-S, in particular in patients with opportunistic bacterial infections.