The radiological effects of peripheral joint disease in 81 patients with seropositive juvenile chronic arthritis were studied retrospectively with an average length of follow up of 11 years. The patients comprised 63 girls and 18 boys with average ages of onset being 10.7 years and 12.1 years respectively. All had developed positive serology within the first year of the disease. X-rays available in 70 of these patients at five years from onset of the disease showed erosive change to be present in all but three. The sites most commonly affected included the carpus, the metacarpal, the metatarsal, and interphalangeal joints, though a third of the patients also showed erosive change in large joints such as hips, knees, or shoulders. Between five and 10 years after disease onset progression of x-ray changes was evident in most patients, with additional joints becoming involved in about one third, though the distribution of joints was similar. After 15 years or more of disease the radiological changes tended to be more stable, but various mechanical difficulties often secondary to poor growth and degenerative change and to primary destructive inflammatory arthritis were evident. No specific drug regimen was found to have been universally effective in suppressing disease, and the frequency of side effects was a significant factor in preventing treatment schedules being maintained for long enough to be effective.