INTRODUCTION: EUROFORS was a 2-yr prospective, randomized trial of postmenopausal women with established osteoporosis, designed to investigate various sequential treatments after teriparatide 20 microg/d for 1 yr. The present secondary analysis examined the effects of 2 yr of open-label teriparatide in women previously treated with antiresorptive drugs for at least 1 yr. METHODS: A subgroup of 245 women with osteoporosis who had 2 yr of teriparatide treatment were stratified by previous predominant antiresorptive treatment into four groups: alendronate (n=107), risedronate (n=59), etidronate (n=30), and non-bisphosphonate (n=49). Bone mineral density (BMD) at the lumbar spine and hip was determined after 6, 12, 18, and 24 months, and bone formation markers were measured after 1 and 6 months. RESULTS: Significant increases in bone formation markers occurred in all groups after 1 month of teriparatide treatment. Lumbar spine BMD increased at all visits, whereas a transient decrease in hip BMD, which was subsequently reversed, was observed in all groups. BMD responses were similar in all previous antiresorptive groups. Previous etidronate users showed a higher increase at the spine but not at the hip BMD. Duration of previous antiresorptive therapy and lag time between stopping previous therapy and starting teriparatide did not affect the BMD response at any skeletal site. Treatment-emergent adverse events were similar to those reported in treatment-naive postmenopausal women with osteoporosis treated with teriparatide. CONCLUSIONS: Teriparatide induces positive effects on BMD and markers of bone formation in postmenopausal women with established osteoporosis, regardless of previous long-term exposure to antiresorptive therapies.