In order to evaluate the effect of long-term, long distance running on the incidence of degenerative joint disease in the lower extremities, we examined the hips, knees, and ankles of 30 long distance runners who had been serious competitive runners in the early 1950s (at the age of 20 to 30 years). Of three runners who were no longer active, one had stopped running in the late 1970s because of osteoarthrosis of both the lower and upper extremity joints. The remaining 27 runners (90%) were still active, having run 20 to 40 km/week (12 to 24 miles/week) for a median of 40 years. Subjective, objective, and roentgenographic data were compared with the data for 27 nonrunning controls matched as to age, weight, height, and occupation. No differences in joint alignment, range of motion, or complaints of pain were found between runners and nonrunners. Roentgenographic examinations for cartilage thickness, grade of degeneration, and osteophytosis were also without significant differences between the two groups. Thus, our observations suggest that a lifetime of long distance running at mileage levels comparable to those of recreational runners today is not associated with premature osteoarthrosis in the joints of the lower extremities.