The Osteoporosis Self-Efficacy Scale was developed as a measure of self-efficacy, or confidence, for behaviors related to physical activity and calcium intake. An item pool of 21 statements, responded to on a visual analog self-report format, was reviewed by a panel of expert judges. The revised item stems were tested with a sample of 201 women, ages 35 to 95. Concurrent data on sport, leisure, and exercise activity and calcium in diet and dietary supplements were collected from the respondents. Factor analysis of responses to the self-efficacy items revealed a logical, theoretically meaningful two-factor structure, one for physical activity and one for calcium intake. Internal consistency estimates for each of the two factors were in the .90s. Convergent and discriminant validity analyses as well as hierarchical regression analyses to explain self-reports of physical activity and calcium intake were supportive. The final version of the brief, psychometrically sound scale contains items reflecting initiation, maintenance, and persistence at osteoporosis preventive behaviors; thus, the Osteoporosis Self-Efficacy Scale is a potentially beneficial research instrument.