Histological and histochemical studies of the spine of a sixteen-year-old boy with juvenile kyphosis who was killed in an automobile accident showed abnormal cartilage in extensive areas of the vertebral and growth plates of the involved vertebrae. In these areas the cartilage matrix was loose, strongly positive when stained with alcian blue and weakly positive to periodic acid-Schiff, and it contained numerous chondrocytes. Some chondrocytes were irregularly shaped and others were in clusters. Vertebral bone growth was stunted under the areas of abnormal vertebral and growth plates. The ossification in the ring apophyses was irregular in areas of abnormal cartilage plate, but necrotic bone was not seen. Schmorl nodes had formed where areas of abnormal cartilage plate adjoining the nucleus pulposus had collapsed, allowing the disc material to herniate into the vertebral body. Clinical Relevance: The defective vertebral-bone formation in juvenile kyphosis appears to result from abnormal vertebral and growth-plate cartilage. The kyphosis and presumably also the cartilage abnormality can be improved during the florid stage of the disease by decreasing the postural load on the anterior part of the vertebrae with the use of a proper brace.