Objective: To evaluate the efficacy and safety of Methimazole in the treatment of hyperthyroidism due to Graves disease in patients younger than 18 years, in Barranquilla in the period January 2013 to April 2015. Materials and methods: Observational analytical study in 20 patients aged 1 to 18 years with confirmed hyperthyroidism due to Graves’ disease in the city of Barranquilla in January 2013 to April 2015 period attending the consultation of pediatric endocrinology (Dr. Jorge Luis Ordonez). Results: Females showed the highest rate with 75 %, mean age of 9.9 ± 2.8 years, goiter was the most frequent sign with 90 %; 100 % of patients admitted with TSH levels < 0.6 μU/ml, with a mean of 0.10 ± 0.25 μU/ml, at 18 months normalization was achieved in 80 % with a mean of 2.80 ± 2.27 μU/ml ( p = 0.0001). Conclusions: Treatment with Methimazole (0.4 mg/kg/day every 8 hours, maintenance 0.2 mg/kg/day every 8 hours; maximum dose: 30 mg) in patients under 18 diagnosed with hyperthyroidism due to illness Graves, is effective, as demonstrated by the appropriate response of TSH and free T4, and by decreasing the frequency of clinical signs.