Oral ibandronate is the first bisphosphonate licensed for once-monthly treatment of postmenopausal osteoporosis. The 2-year Monthly Oral iBandronate In LadiEs (MOBILE) registration study assessed bone mineral density (BMD) and markers of bone turnover and showed that monthly oral ibandronate was at least as effective and well tolerated as a 2.5-mg daily oral regimen. In this study, we report the first year of a long-term extension study to MOBILE and a post hoc analysis of patients receiving 3 years of continuous treatment with monthly ibandronate. Patients who completed MOBILE were eligible for the partially randomized, double-blind extension study and received 100 mg (n = 359) or 150 mg (n = 360) monthly oral ibandronate. A post hoc analysis included patients who received either 100 mg (n = 173) or 150 mg (n = 169) monthly ibandronate continuously throughout the original 2-year MOBILE study and during the first year of the extension study. After one additional year of treatment (total of 3 years), mean lumbar spine BMD increased a further 1.5 and 1.1% in the 150 and 100 mg arms, respectively, compared with 2-year data (original MOBILE study). Total hip BMD changed by 0.3 and -0.08%, respectively. In the post hoc analysis, 3-year increases in lumbar spine BMD were significant in patients receiving ibandronate 150 mg monthly (7.6%; p < 0.0001 vs. baseline) and 100 mg monthly (6.4%; p < 0.0001 vs. baseline). Both groups achieved significant increases in total hip BMD after 3 years compared with baseline (3.4%, 100 mg; 4.1%, 150 mg; p < 0.0001). Serum C-telopeptide of the alpha chain of type I collagen decreased significantly over 3 years' treatment (p < 0.001; all comparisons vs. baseline), remaining within the premenopausal range. Once-monthly oral ibandronate was well tolerated with a low incidence of clinical osteoporotic fractures and upper gastrointestinal events. In conclusion, 150-mg monthly oral ibandronate is an effective and well-tolerated long-term treatment for postmenopausal osteoporosis, with consistent improvement in BMD and bone turnover during 3 years' continuous treatment.