Acromegaly is associated to thyroidal disorders such as hyperthyroidism. The Graves-Basedow disease as a cause of thyroid hyperfunction is very infrequent, with only 8 cases having been reported up to 1993. The authors present 3 patients with acromegaly who developed hyperthyroidism due to Graves-Basedow disease in the course of their disease. Two of the patients had acromegaly of 30 years of evolution and the third patient underwent consultation for clinical symptoms of hyperthyroidism with acromegaly being simultaneously diagnosed. All the patients had weight loss prior to diagnosis and the possibility of neoplasia associated to acromegaly was excluded. The hyperthyroidism responded well to initial treatment with antithyroid drugs in the three cases. The authors conclude that hyperthyroidism should be taken into consideration in the diagnosis of a patient with acromegaly and weight loss.