Abstract: The aim of this study was to assess the prevalence of densitometric osteoporosis and vertebral fractures in Spanish men aged ?50 years, and to study how the relationship between them may change depending on how osteoporosis is diagnosed. A community-based population of 1003 men aged ?50 years was studied. Bone mineral density (BMD) was measured by DXA at the lumbar spine, femoral neck and total hip. Vertebral fractures were assessed by lateral thoracic and lumbar spine radiographs. The prevalence of osteoporosis was estimated with both the World Health Organization (WHO) (T-score of <-2.5 at the femoral neck, calculated using the young white female normal reference database) and the National Osteoporosis Foundation (NOF) criteria (T-score of <-2.5 at the femoral neck, total hip or lumbar spine, calculated using the young white male normal reference database). The prevalence of osteoporosis using the WHO criterion was 1.1% and using the NOF criterion was 13%, while that of vertebral fractures was 21.3%. The area under the curve (AUC) for the relationship between BMD and vertebral fracture prevalence was 0.64. The odds ratio for osteoporosis using the WHO definition was 2.57 (p = 0.13), and 1.78 (p = 0.007) using the NOF definition. Vertebral fracture prevalence rose with age. The prevalence of osteoporosis increased only moderately in men aged >70 years with the WHO criterion, and showed no change using the NOF definition. The prevalence of osteoporosis in Spanish men using the WHO definition is too small to have any meaningful clinical use. Although the figure is higher using the NOF definition, it would seem that population-based studies of BMD in men are of questionable value.