The present study was made on a specimen removed at autopsy. The patient was reported to have died of diabetes mellitus. During the progress of the autopsy, the knee was discovered to be slightly swollen. Clinical symptoms of trouble with the knee were not recorded, but when the knee was opened, a typical instance of osteochondritis dissecans was found. The discovery of loose bodies within a joint, especially the knee, has been of great clinical interest, both in respect to the origin of these bodies and as regards treatment. Various names have been used to describe them, such as "joint mouse," "loose body," "floating body" and others. There are several varieties, namely, those which result from a disease process, such as tuberculosis, tabes or pus infection; those which follow definite trauma, wherein a portion of bone and cartilage is broken off; those which result from proliferative changes in the cartilage