Abstract: In order to study a possible relation between mechanical bone pains and the BMD, 1335 patients were analyzed as every consecutive patient. The BMD was measured in a cohort study on 5927 patients referred for various reasons to the Rheumatology Research Center, Osteoporosis Unit. The BMD was measured by Dual Energy X-rays Absorptiometry (DEXA) on the lumbar spine (L1-L4) and the femoral neck. Patients having an inflammatory disease such as rheumatoid arthritis or an endocrine disease such as hyperthyroidism or diabetes mellitus and patients taking drugs with known effect on bone mass were discarded. A total of 1335 patients fulfilled the selection criteria. Their BMD was compared with normal range of Iranians (age and sex matched) by Chi square test and the mean difference was calculated. In the lumbar spine a decrease of 4.3% (SD=2.5, CI=0.07) was demonstrated totally in the cohort study, while it was only 1.7% (SD=2.5, CI=0.13) in patients with non inflammatory diseases. In the femoral neck the decrease in the total patients was 5.5% (SD=2.69, CI=0.03), but it was 2.9% (SD=1.96, CI=0.09) in the non inflammatory group. Conclusion: Abnormal reduction on BMD is mainly caused by inflammatory diseases and mechanical disorders are not a stigma of osteoporosis (at least in the majority of the patients). This study warrants the importance of measuring the BMD in people at risk, as the reduction of BMD is usually silent until a fracture appears.