A case of 67-year-old woman with hyperthyroidism due to functioning thyroid adenoma is reported. The patient had concomitant follicular thyroid adenoma and primary hyperparathyroidism in addition to functioning adenoma. Histological examination of the excised thyroid tissue revealed occult papillary carcinoma within a functioning adenoma. Genetic analysis of such tumors indicated that functioning adenoma and papillary carcinoma may be etiologically independent. There have been a number of case reports on the coexistence of functioning thyroid adenoma and thyroid cancer or hyperparathyroidism, but none of the studies had examined the etiologic relationship of these lesions on a genetic basis. Furthermore, to our knowledge, this is the first report of the concurrence of four tumors in the neck, functioning thyroid adenoma, papillary thyroid carcinoma, follicular thyroid adenoma and parathyroid adenoma.