Objectives: To validate osteoporosis risk assessment tools in middle-aged Thai women. Methods: A total of 1038 women who had bone mineral density (BMD) measurements using dual energy X-ray absorptiometry were reviewed. Clinical data were used to validate the diagnostic test performance of various osteoporosis risk assessment tools, including ABONE, FRAX (R), ORAI, OSIRIS, SCORE, SOFSURF, and OSTA. The following parameters were evaluated: sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV), and accuracy; those with 95% confidence interval (CI) of the receiver operator characteristics area under the curve (ROC-AUC) > 0.5 were considered statistically significant. Results: The subjects had a mean age of 53.01 +/- 6.20 years and body mass index (BMI) of 23.98 +/- 3.38 kg/m(2). Among the osteoporosis risk assessment tools being evaluated, the tools that had ROC-AUC >0.8 and 95% CI >0.5, and could predict osteoporosis at the femoral neck with high specificity of >75% and NPV of >90%, were FRAX (R) without BMD (ROC-AUC 0.83; 95% CI 0.73-0.93; specificity 99.90; NPV 98.89), SCORE (ROC-AUC 0.86; 95% CI 0.78-0.94; specificity 98.79; NPV 98.99), and OSTA (ROC-AUC 0.86; 95% CI 0.79-0.94; specificity 75.03; NPV 99.73). Conclusion: The prevalence of osteoporosis in the middle-aged Thai women attending Siriraj Menopause Clinic is 7.3% at the lumbar spine and/or femoral neck. FRAX (R) without BMD, SCORE, and OSTA have appropriate validity as tools for ruling out osteoporosis in these women.