Hashitoxicosis is generally differentiated from Graves' hyperthyroidism by its shorter course and absence of ophthalmopathy. In this case report, we describe an adolescent girl who presented with significant clinical findings of hyperthyroidism, a diffuse goiter with homogenously increased uptake in scintigraphy, and with ocular findings of ophthalmopathy. The thyroid stimulating hormone receptor antibody test was positive, and the family history revealed thyroid-associated ophthalmopathy. Clinical findings supported the diagnosis of Hashimoto's disease (HD) in the follow-up period. Radioactive iodine uptake investigation was found to be a reliable method for differential diagnosis. Attention was drawn to the rarity of pediatric cases of HD who present with ophthalmopathy.