BACKGROUND: The aim of this study was to investigate the demographic and clinical characteristics of patients with primary frozen shoulder in a Korean population. METHODS: A total of 1,373 patients whose shoulders were diagnosed with primary frozen shoulder across 11 resident-training hospitals were reviewed retrospectively. Various demographic characteristics and clinical characteristics according to gender and presence of diabetes were evaluated. RESULTS: The average age of patients was 55.4 years. Gender proportion was 58.3% females and 41.7% males. The frozen shoulder involved the non-dominant arm in 60.7% of patients and the bilateral arms in 17.6% of patients. The average duration of symptoms was 8.9 months, and 51.3% of patients had experienced nocturnal pain. Comorbidities associated with frozen shoulder in our sample of patients included diabetes (18.7%), cardiovascular diseases (17.7%), thyroid diseases (5.4%), and cerebrovascular diseases (3.6%). The diabetic group was correlated with the following demographic and clinical characteristics: old age, involvement of the dominant arm, nocturnal pain, long duration of symptoms, and no history of trauma. Further, we found that, in males, having a frozen shoulder was significantly correlated with a history of trauma; in females, having a frozen shoulder was significantly correlated with having thyroid diseases. CONCLUSIONS: These demographic data of primary frozen shoulder in the Korean population were consistent with those of previously reported epidemiologic studies. Primary frozen shoulder with diabetes was correlated with old age, bilateral involvement, long duration of symptoms, and nocturnal pain.