Megacolon occurs frequently in high altitude areas. This report describes observations made in 60 cases seen in La Paz, Bolivia (3,600 meters above sea level). Motility of both the large and small bowel was found to be increased and the feces had a low pH. No histologic abnormalities were noted in the nervous plexus or smooth muscle. It is assumed that megacolon in these circumstances is acquired and not congenital.