BACKGROUND Clinical cases of nonmedullary thyroid carcinoma (NMTC) in combination with primary hyperparathyroidism (PHPT) have been reported occasionally. However, the clinical characteristics and risk factors of concomitant NMTC in PHPT patients remain unclear. This study aimed to assess the association between PHPT and NMTC, and evaluate the clinical characteristics and risk factors of NMTC in Chinese patients with PHPT. MATERIAL AND METHODS This was a retrospective cohort analysis. We reviewed the medical records of 155 patients who underwent surgery for PHPT in two large medical centers in China between 2009 and 2014. The clinical manifestations, biochemical abnormalities, and histological characteristics of PHPT patients were analyzed. RESULTS Of the 155 patients with PHPT, 58 patients (37.4%) had thyroid nodules and 12 patients (7.7%) were ill with concomitant NMTC. PHPT patients with NMTC demonstrated significantly lower preoperative serum calcium levels compared to PHPT patients with benign thyroid nodules (p<0.05). A significantly negative association between preoperative serum calcium levels and the presence of NMTC was found in PHPT patients (p<0.05). Furthermore, ROC analysis revealed that albumin-corrected serum calcium levels <2.67 mmol/L had good capacity to differentiate the PHPT patients with NMTC from those with benign thyroid nodules. CONCLUSIONS Compared with the reported much lower prevalence of thyroid carcinoma in the general population, our results suggest that PHPT might be a risk factor for the malignancy of thyroid nodules; a lower level of serum calcium may predict the existence of NMTC in PHPT patients with thyroid nodules.