Objective：To investigate the value of 11C-choline positron emission tomography/computed tomography（PET/CT） in the pre－operative localization diagnosis of difficult cases of primary hy－perparathyroidism（PHPT）. Methods：A total of 92 patients with PHPT（including 21 male patients aged 54.2±14.1 years） who planned to undergo surgical treatment and had difficulties in localization after ultrasound and 99mTc-MIBI were enrolled. PET/CT was performed at 20 minutes after the intravenous in－jection of 111-333MBq（3-9mCi）11C-choline. Visual and quantitative methods were used for image analysis，and with pathological results as the gold standard，PET/CT findings were compared with the results of serological examination. IBM SPSS 23 was used for statistical analysis. Results：A total of 103 lesions were detected by 11C-choline PET/CT in 92 patients，among which there were 83 lesions of parathyroid adenoma or hyperplasia，5 lesions of parathyroid carcinoma or its metastatic lesions，4 lesions of pulmonary neuroendocrine tumor，7 lesions of nodular goiter，and 4 lesions of metastatic lesions of medullary thyroid carcinoma；86 lesions were strongly positive and 17 were weakly positive. One lesion of cystic degeneration of parathyroidoma and one of parathyroid tissue were not detected. 11C-choline PET/CT had an overall sensitivity of 98.9%，a specificity of 6.3%，an accuracy of 84.8%，a positive predictive value of 85.4%，and a negative predictive value of 50%. The 78 strongly positive lesions of PHPT had significantly higher maximum standard uptake value（SUVmax） and standardized uptake value（SUV） ratio than the 10 weakly positive lesions（SUVmax：3.95（2.77，7.73） vs. 2.60（1.95，4.42），P=0.036；SUV ratio：1.72（1.43，2.42） vs. 1.19（1.11，1.51），P=0.002）. There were no significant differences between the PHPT group and the non-PHPT group in blood PTH，serum calcium，and serum phosphate（P=0.115，0.217，and 0.901）. Conclusion：11C-choline PET/CT can be used for preoperative local－ization diagnosis of PHPT，with a high sensitivity and a poor specificity. The differentiation of PHPT from nodular goiter and malignant tumor should be taken seriously in clinical practice.