Objective: To report a case of parathyromatosis as a cause for recurrent hyperparathyroidism. Methods: We present the case history, laboratory results, operative interventions, and pathologic findings in a 36-year-old woman. Relevant reports from the literature are reviewed. Results: Our patient, who had been undergoing long-term hemodialysis because of renal failure, presented with secondary hyperparathyroidism and progressive bone pain. After an uneventful subtotal parathyroidectomy (removal of 31/2 glands), her symptoms resolved in conjunction with normalization of parathyroid hormone levels. Subsequently, however, recurrent hyperparathyroidism and severe bone pain necessitated second and third neck explorations, during which parathyromatosis was discovered. A total thyroidectomy was performed because of the bilateral nature of the disease. Postoperatively, the patient's bone pain resolved substantially, although her parathyroid hormone levels remained high. Conclusion: Parathyromatosis is a rare cause of recurrent hyperparathyroidism after parathyroidectomy. It consists of hyperfunctioning parathyroid tissues scattered throughout the neck, due either to intraoperative tissue spillage and subsequent implantation or to hyperplasia of parathyroid rests from embryologic development. This is one of the few case reports of parathyromatosis and the first case report of a mixed form of the disease, consisting of features of both subcapsular parathyroid rests and extracapsular implantation.