© 2019, International Osteoporosis Foundation and National Osteoporosis Foundation. Summary: The Osteoporosis Self Efficacy Scale was determined to equivalently measure calcium and exercise beliefs in both sexes. Despite data illustrating men’s and women’s similar self-efficacy, gender differences in clinical predictors of self-efficacy imply that efforts to improve care must account for more than self-efficacy. Introduction: To understand the extent to which the Osteoporosis Self Efficacy (OSE) Scale is reliable for both men and women. A secondary objective was to evaluate sex differences in OSE. Methods: For this cross-sectional study, we analyzed data collected as part of the Patient Activation after DXA Result Notification (PAADRN) pragmatic trial which enrolled 7749 community-residing adults aged 50 and older reporting for bone densitometry. We used univariable methods, item analysis, exploratory and confirmatory factor analyses, and linear regression to evaluate sex differences in OSE responses and measurement. Results: In this sample, the confirmatory factor analysis model for OSE both overall and within groups indicated a poor fit. The sex differences in the measurement model, however, were minor and reflected configural invariance (i.e., constructs were measuring the same things in both men and women), confirming that the OSE was measuring the same constructs in men and women. Men overall had higher exercise self-efficacy and women higher calcium self-efficacy. Overall, education, hip fracture, and self-reported health status predicted exercise self-efficacy whereas prior DXA, self-reported osteoporosis, and history of pharmacotherapy use did not. Predictors of calcium self-efficacy differed by gender. Conclusion: The OSE can be used to measure calcium and exercise self-efficacy in all older adults. However, gender differences in clinical predictors of self-efficacy and the lack of an association of prior DXA with self-efficacy imply that interventions to improve self-efficacy may be insufficient to drive significant improvement in rates of osteoporosis evaluation and treatment. Trial registration: Patient Activation after DXA Result Notification (PAADRN), NCT01507662, https://clinicaltrials.gov/ct2/show/NCT01507662.