OBJECTIVES: To reassess the safety and efficacy of once-weekly teriparatide 56.5 μg in osteoporosis patients with a high fracture risk. METHODS: This postmarketing observational study was conducted at 72 weeks according to the package insert. Of the 3573 Japanese osteoporosis patients in the safety analysis set, 91.80% were women, the mean age was 78.1 years, and 69.89% had a history of prevalent fragility fractures, indicating that a high proportion of patients at high risk of fracture were enrolled. RESULTS: Persistence with weekly teriparatide treatment was 59.36%, and 38.95% at 24 and 72 weeks, respectively. Adverse drug reactions (ADRs) were reported in 898 patients (25.13%), and serious ADRs were reported in 26 patients (0.73%). The most frequent ADRs were nausea, vomiting, and headache. The cumulative incidence of new vertebral fractures 72 weeks after the start of treatment was 3.31%. Increases in the bone mineral density were observed in the lumbar spine, femoral neck, and proximal femur. The serum levels of the bone formation markers, procollagen type I N-terminal propeptide and bone-type alkaline phosphatase, increased slightly at 24 weeks and then decreased to baseline levels. At 24 and 72 weeks, the bone resorption markers, serum cross-linked N-terminal telopeptide of type I collagen and urinary cross-linked N-terminal telopeptide of type I collagen, were the same as or slightly lower than at baseline. Visual analogue scale scores for low back pain also decreased. CONCLUSIONS: The present results showed that once-weekly teriparatide may also be useful for osteoporosis patients with a high risk of fracture.