Graves' disease is the most common reason of hyperthyroidism in children. Graves' disease with accompanying functioning nodules is defined as Marine-Lenhart syndrome. This syndrome has not been described in children before. Here, a 15-year-old girl with Graves' disease and a coexisting cold nodule is presented. A thyroid scan showed diffuse uptake of Tc-99m pertechnatate in both lobes and decreased uptake in accordance with the left lobe nodule. The nodule was histologically diagnosed as benign. The patient was diagnosed with type 1 diabetes mellitus and polyglandular autoimmune syndrome during clinical follow-up. The differential diagnoses of Graves' disease with coexisting nodules should include the Marine-Lenhart syndrome. Treatment options should be determined taking this rare condition into account.