In this 2-yr randomized controlled trial, we examined the effect of bone mineral density feedback and two different educational interventions (an osteoporosis information leaflet and group-based behavioral education [OPSMC]) on osteoporosis knowledge and self-efficacy in 470 women aged 25-44 yr. Osteoporosis knowledge increased across all intervention groups. Women receiving the OPSMC had a greater increase in both short (beta = +1.33, 95% confidence interval [CI] = 0.72-1.94) and long-term (beta = +0.64, 95% CI = 0.0034-1.25) osteoporosis knowledge, compared to those receiving the leaflet. In contrast, a low T-score was associated with a significant increase in long-term (beta = +0.66, 95% CI = 0.0034-1.25) but not short-term (beta = +0.57, 95% CI = -0.036 to 1.17) osteoporosis knowledge, compared to a normal T-score. Changes in osteoporosis self-efficacy were not associated with either low bone mineral density or receiving the OPSMC but were negatively associated with number of children (beta = -0.9, 95% CI = - 1.4 to -0.3) and working more than 20 h per week (beta = -2.7, 95% CI = -4.6 to -0.8). In conclusion, both the OPSMC and bone density feedback increased osteoporosis knowledge but not self-efficacy over 2 yr. Women with children or who worked full time have decreased osteoporosis self-efficacy, suggesting that this group should be a specific target for future interventional strategies.