PURPOSE: To identify factors associated with early treatment discontinuation of three agents commonly prescribed for women with low bone density. METHODS: A telephone survey was conducted in 2000 to 2001 in a random sample of women aged 45 years or older who had bone density T-scores -1.0 or lower and who had initiated treatment with hormone replacement therapy, raloxifene, oral endronate. Logistic regression was used to estimate adjusted odds ratios for early treatment discontinuation. RESULTS: Among 956 women who were interviewed an average of 7 months after treatment initiation, 334 were taking hormone therapy, and 88 (26%) had discontinued; 256 were taking raloxifene, and 48 (19%) had discontinued (P = 0.03 vs. hormone therapy); and 366 were taking alendronate, and 70(19%) had discontinued (P = 0.02 vs. hormone therapy). Women with bothersome side effects (somewhat bothered: odds ratio [OR] = 4.0; 95% confidence interval [CI]: 2.5 to 6.5; very or extremely bothered: OR = 25; 95% CI: 16 to 39) or who thought that their bone density test results did not show osteoporosis (OR = 1.6; 95% CI: 1.0 to 2.5) were more likely to discontinue therapy, as compared with women reporting regular exercise (OR = 0.7; 95% CI: 0.4 to 1.0) or a willingness to take prescribed medications (OR = 0.6; 95% CI: 0.4 to 0.9). After adjustment for side effects and patient characteristics, the odds of early treatment discontinuation did not differ significantly among treatments. CONCLUSION: Improved adherence to osteoporosis treatment requires that treatment side effects be minimized and women be educated regarding their bone density test results.