Background: The etiology of idiopathic adhesive capsulitis (IAC) of the shoulder is poorly understood. In this case control study, we examine potential risk factors for the development of IAC. Methods: Consecutive patients who presented to the senior author with IAC between 2000 and 2009 were included retrospectively in this case control study. Complete data were available for 87 patients. An age- and sex-matched group of 176 patients who presented to the same practice during the same time period with non-shoulder related orthopedic complaints were recruited as the control group. Health records and patient-completed questionnaires were utilized to identify comorbidities and other risk factors. Results: Bivariate analyses demonstrated that diabetes, hypothyroidism, a lower body weight, a lower body mass index (BMI), and a positive family history of IAC were all risk factors for IAC. Diabetes, BMI, and positive family history of IAC remained independent variables with multivariate logistic regression analyses. There was a trend towards increased incidence of Dupuytren s disease in those with IAC, but this was not statistically significant. With regard to racial predilection, being born in the British Isles or having parents/grandparents born in the British Isles were risk factors for IAC. Conclusion: We confirm diabetes as an independent predictor of IAC. In addition, we identify a possible racial predilection for the development of IAC. Future research is needed to confirm whether a specific genetic component or environmental factors is responsible. ? 2013 Journal of Shoulder and Elbow Surgery Board of Trustees.