Objectives: To describe the clinical and biochemical response to treatment of hyperthyroidism. Design: Retrospective study. Setting: Instituto Nacional de Salud del Niño, Lima, Peru. Participants: children. Methods: From 1996 to 2007 32 patients with diagnosis of hyperthyroidism were studied. Remission was defined when patients were asymptomatic and biochemically euthyroid 6 months after the end of treatment; relapse when altered hormone levels were found after this period of time. Main outcome measures: Remission or relapse following treatment. Results: Mean age at diagnosis was 10.5 years (3.2-17.9 years), 26 patients (81.2 %) were female; 13 (40.6 %) were pubertal and 18 (59.3%) prepubertal. The most frequent symptoms and signs were: goiter, sweating, nervousness, weight loss, tachycardia and exophthalmos. Methimazole was used as first therapeutic option. Initial dose was 0.78mg/kg/d...