PURPOSE: To investigate whether bone mineral density(BMD) occurs in association with fatty replacement oflower paraspinal muscles and whether it relates with the area ratio(Ps/V) of psoas muscle(Ps) divided by adjacentvertebral body(V). MATERIALS AND METHODS: For the evaluation of osteoporosis, 100 females underwent quantitativeCT. At L1,L2 and L3 levels, the fatty replacement of lower paraspinal muscles was numerically graded and therelationship between this and BMD of the vertebral body was evaluated. The correlation between BMD and Ps/V at L2and L3 levels was also evaluated, as was the relationship between the thickness of subcutaneous fat tissue at L1,L2 and L3 levels. RESULTS: BMD showed significant inverse correlations with the grade of the fatty replacement oflower paraspinal muscles at L1(p<.01), L2 level and L3 level(p<.001). In particular, significant differenceswere established between grade 0 and 2 (p<.05) at L1 level, and between grade 0 and 2, and 1 and 2 (p<.05) at L2and L3 levels. There was markedly low correlation (gamma=.33) between BMD and Ps/V at L3 level(p<.001) and lowercorrelation (gamma=.22) at L2 level(p<.05). At L2 and L3 levels, there was no correlation between the thickness ofsubcutanous fat tissue and BMD or Ps/V. CONCLUSION: The present study demonstrates that there was significantinverse correlation between BMD and fatty replacement of lower paraspinal muscles, and low correlation between BMDand Ps/V.