A 14 year-old girl with a previous medical history of cholecystic polyps was referred to our department with throat discomfort during swallowing. The cervical ultrasound and magnetic resonance imaging revealed a massive polycystic formation with a diameter of 45 × 24 × 31 mm consistent with a right lobe goiter. However, there were no findings for suspected malignancy. Hemithyroidectomy was performed and the specimen was sent for histopathological assessment. Hematoxylin-eosin staining of the right lower nodule showed variably-sized follicles consistent with adenomatous goiter. The right upper nodule showed a growth of relatively compact sized follicles with a thick fibrous capsule. A satellite nodule lying outside of the tumor capsule was consistent with minimally invasive follicular thyroid microcarcinoma. We observed her without any additional treatment and no recurrence is seen at present.