Diverging international trends in fracture rates have been observed, with most reports showing that fracture rates have stabilized or decreased in North American and many European populations. We studied two complementary population-based historical cohorts from the Province of Manitoba, Canada (1996–2006) to determine whether declining osteoporotic fracture rates in Canada are attributable to trends in obesity, osteoporosis treatment, or bone mineral density (BMD). The Population Fracture Registry included women aged 50 years and older with major osteoporotic fractures, and was used to assess impact of changes in osteoporosis treatment. The BMD Registry included all women aged 50 years and older undergoing BMD tests, and was used to assess impact of changes in obesity and BMD. Model-based estimates of temporal changes in fracture rates (Fracture Registry) were calculated. Temporal changes in obesity and BMD and their association with fracture rates (BMD Registry) were estimated. In the Fracture Registry (n = 27,341), fracture rates declined 1.6% per year (95% confidence interval [CI], 1.3% to 2.0%). Although osteoporosis treatment increased from 5.6% to 17.4%, the decline in fractures was independent of osteoporosis treatment. In the BMD Registry (n = 36,587), obesity increased from 12.7% to 27.4%. Femoral neck BMD increased 0.52% per year and lumbar spine BMD increased 0.32% per year after covariate adjustment (p < 0.001). Major osteoporotic fracture rates decreased in models that did not include femoral neck BMD (fully adjusted annual change –1.8%; 95% CI, –2.9 to –0.5), but adjusting for femoral neck BMD accounted for the observed reduction (annual change –0.5%; 95% CI, –1.8 to +1.0). In summary, major osteoporotic fracture rates declined substantially and linearly from 1996 to 2006, and this was explained by improvements in BMD rather than greater rates of obesity or osteoporosis treatment. © 2014 American Society for Bone and Mineral Research.