We present a case of a parathyroid adenoma on the ipsilateral side of thyroid hemiagenesis-which, to our knowledge, is the third reported case of this entity. A 41-year-old man with nephrolithiasis was found to have elevated calcium and intact parathyroid hormone levels. Both ultrasound and technetium sestamibi scintigraphy with single photon emission computed tomography confirmed left thyroid hemiagenesis and an adenoma in the left inferior thyroid bed. The patient underwent left neck exploration, which confirmed left thyroid hemiagenesis and a left inferior parathyroid adenoma. The left inferior parathyroid gland was resected. The patient was discharged home the same day of surgery and has remained normocalcemic for 14 months without evidence of hyperparathyroidism.