Simultaneous existence of parathyroid adenoma and thyroid nonmedullary carcinoma is rarely observed. A 52-year-old female was diagnosed approximately 4 years ago with primary hyperparathyroidism (PHPT) on the basis of hypercalcemia and elevated serum parathyroid hormone (PTH) level. Clinically, PHPT diagnosed patient was examined with Tc-99m MIBI scintigraphy to investigate parathyroid adenoma. Early Tc-99m MIBI images showed focal focused enhanced activity retention on both thyroid left lobe upper pole and thyroid lower pole inferior neighborhood. However, late images indicated thyroid activity washout and persistence of activity on left lobe lower pole. The observed lesion on left lobe lower pole neighborhood was identified as parathyroid adenoma. One-day thyroid scintigraphy was also conducted to correlate enhanced activity retention on the left lobe upper pole. Results on thyroid scintigraphy showed hypoactivity, and thyroid fine-needle aspiration cytology process was suggested from the nodule. Simultaneous existence of parathyroid adenoma and thyroid nonmedullary carcinoma is rarely observed. Diagnosis and treatment of hyperparathyroidism is crucial during preoperative period. Even observed rarely, parathyrotoxicosis diagnosed patients can develop thyroid cancer along with parathyroid adenoma.