Hashimoto's thyroiditis is a known autoimmune disorder that leads to chronic inflammation of the thyroid gland, with a gradual decline in function and eventual hypothyroidism. Conversion of Hashimoto's thyroiditis to Graves' disease is unusual clinically and has been occasionally reported in the literature. Awareness of such a rare phenomenon is important for the physicians evaluating patients with autoimmune thyroid disorders. Close investigation of the patient's symptoms and biochemical status is crucial in the implementation of appropriate treatment.