Thyroid hemiagenesis is a rare congenital anomaly in which one thyroid lobe fails to develop. We recently observed a case of thyroid hemiagenesis accompanied by parathyroid adenoma and papillary thyroid microcarcinoma in a 51-years-old woman. The patient's serum calcium level was 10.9 mg/dL and that of intact parathyroid hormone was 218 pg/mL. Although she had a history of thyroid hemiagenesis, the patient was in a euthyroid state without thyroxine replacement. Thyroid ultrasonography detected no right lobe and four nodules of varying sizes in the left thyroid lobe. Tc-99m scintigraphy also demonstrated the absence of the right thyroid lobe. In addition, MIBI-parathyroid scintigraphy showed a parathyroid adenoma at the lower pole of the right cervical region. Based on the diagnosis, parathyroid adenoma excision and thyroidectomy were performed. Postoperative pathological diagnosis revealed parathyroid adenoma and papillary thyroid microcarcinoma in the form of a 0.4 cm sized tumor in the left thyroid lobe. The coexistence of thyroid hemiagenesis, primary hyperparathyroidism, and papillary thyroid microcarcinoma is truly exceptional and has never been reported in the literature before.