Hyperthyroidism in children and adolescents usually is due to Graves disease. The diagnosis may not be recognized promptly, and clinical findings initially may be attributed incorrectly to cardiac or psychological disorders. Once suspected, history and physical findings and measurements of TSH level, thyroid hormone levels, and thyroid antibodies make the diagnosis apparent. Treatment varies among endocrinologists and includes antithyroid medication, surgery, and radioactive iodine. Much is being learned about the autoimmune response that causes the disease, and the hope is that therapies directed at altering the autoimmune abnormalities ultimately will offer the best therapeutic alternatives.