Nonmedullary thyroid carcinoma was diagnosed in three of nine cases of primary hyperparathyroidism, In all three cases, diagnosis of primary hyperparathyroidism was made before that of thyroid carcinoma, In the first case, follicular carcinoma was incidentally detected during parathyroidectomy, In the second case, thyroid tumor was discovered during imaging studies for hyperparathyroidism. Papillary carcinoma and ectopic parathyroid was diagnosed postoperatively. In the third case, a thyroid lesion had been mistaken for a putative parathyroid lesion, but the diagnosis of papillary carcinoma was obtained. These cases suggest that preoperative examination for hyperparathyroidism should be carefully evaluated, considering possible concomitant thyroid lesions.