Teriparatide increases skeletal mass, bone turnover markers, and bone strength, but local effects on bone tissue may vary between skeletal sites. We used positron emission tomography (PET) to study 18F-fluoride plasma clearance (Ki) at the spine and standardized uptake values (SUVs) at the spine, pelvis, total hip, and femoral shaft in 18 postmenopausal women with osteoporosis. Subjects underwent a 1-hour dynamic scan of the lumbar spine and a 10-minute static scan of the pelvis and femurs at baseline and after 6 months of treatment with 20 µg/day teriparatide. Blood samples were taken to derive the arterial input function and lumbar spine Ki values evaluated using a three-compartment model. SUVs were calculated for the spine, pelvis, total hip, and femoral shaft. After 6 months treatment with teriparatide, spine Ki values increased by 24% (p = .0003), while other model parameters were unchanged except for the fraction of tracer going to bone mineral (k3/[k2 + k3]), which increased by 23% (p = .0006). In contrast to Ki, spine SUVs increased by only 3% (p = .84). The discrepancy between changes in Ki and SUVs was explained by a 20% decrease in 18F− plasma concentration. SUVs increased by 37% at the femoral shaft (p = .0019), 20% at the total hip (p = .032), and 11% at the pelvis (p = .070). Changes in bone turnover markers and BMD were consistent with previous trials. We conclude that the changes in bone formation rate during teriparatide treatment as measured by 18F− PET differ at different skeletal sites, with larger increases in cortical bone than at trabecular sites. © 2011 American Society for Bone and Mineral Research.