An extremely rare case of metachronous primary hyperparathyroidism (PHP) due to a parathyroid adenoma and subsequent carcinoma with local lymphatic spread is presented herein. A 55-year-old woman was operated on for a parathyroid adenoma in the right inferior gland. Thirteen years after the first operation, she was again hospitalized for hypercalcemia and the presence of a hard mass in the right anterior neck region. Exploratory surgery and a histological examination of the resected tumor provided evidence of a parathyroid neoplasm in the right superior gland but the malignancy was equivocal. Postoperatively, her serum parathyroid hormone (PTH) level remained at 1.5-fold the upper limit of the normal range, and hypercalcemia again gradually developed. The results of higher positive rates by Ki-67 immunohistochemical staining and an aneuploid pattern by a flow cytometric analysis of the second neoplasm were consistent with a histological diagnosis of carcinoma, and she therefore underwent further surgery. A radical neck dissection revealed two lymph node metastases which were both successfully removed. The postoperative serum PTH and calcium levels then returned to within the normal ranges. These findings indicate the usefulness of Ki-67 immunohistochemical staining and a flow cytometric analysis for differentiating malignant lesions from benign parathyroid lesions, and the importance of surgically treating cases limited to local regions without distant metastasis.