Aprospective study on 23 patients with American visceral leishmaniasis (VL), comparing clinical and laboratory parameters of 14 children (mean age of 3.85±3.39 years) to nine adults (27.4±10.90 years) was performed in S˜ao Lu´ıs, Maranh˜ao, Brazil, between August 2000 and July 2002. Data were collected at entrance (day 0), end of treatment, as well as 120 and 210 days after treatment using a protocol chart containing patient identification, clinical and laboratory data. N-Methylglucamine antimonate administered at the dose of 20 mg/Sb5+/kg/day for 20–30 days was successfully used in all patients. Patients were followed for 1 year after treatment, and no relapses were observed. A prolonged duration of the disease, lymphadenopathy and bleeding predominated in adult patients, while hepatomegaly and skin-mucosal pallor were more frequent in children. Disease was longer and more severe in adults than in children. Although both groups exhibited a trend toward normalization of hematological and biochemical parameters, more children returned sooner to normal values than adults. Difference in clinical or laboratory parameters between children and adults did not indicate the need for different clinical or therapeutic approaches.