It is generally believed that this disease is a degenerative process, a part of the general ageing phenomena, hastened by excessive functional demand and a decreasing efficiency of blood supply. Though degenerative joint disease is the commonest of all ailments, its manifestations do not appear as a rule until the fourth or fifth decade, and it is not always easy to diagnose because we know less about it than about many less common types. Little information is available on its frequency in persons below the age of forty. The present study was designed to obtain more precise information about development of this disease in person below the age of forty. After a detailed clinical examination, X-ray findings of a total of 566 men with low back pain checked at the Department of Radiology, National Police Hospital from Jan. 1976 to Dec. 1978 were reviewed. 1. 111 (19.6%) of the 566 men had radiologic evidence of degenerative disease in lumbar spine. The degenerative joint disease f rst appeared on the age of 26. The degenerative joint disease was found in 16 (14.9%) of the 107 men between 25 and 29 years old, 14 (16.3%) of the 86 men between 35 and 39 years old, 31 (27.4%) of the 113 men between 35 and 39 years old, and 50 (50%) of the 100 between 40 and 44 years old. 2. The 4th lumbar spine was most commonly involved, being in 82.0% of the cases, and less frequent sites were the 5th lumbar spine (67.6%), the 3rd lumbar spine (51.3%), the 2nd lumbar spine (18.9%) and the 1st lumbar spine (3.6%). 38 (28.8%) of the 111 cases revealed single level involvement, but 79 (71.2%) cases showed multiple level involvement with the highest incidence at 14 and 15. 3. 111 cases of the 566 revealed marginal spurring. Bridging was noted in 8 cases, space narrowing 8 cases, and eburnation 7 cases.