From 1985 to 1991, 623 cases of supracondylar fracture of the humerus in children were admitted to one center, of which 403 were analyzed in detail. Of these, 180 cases were classified as Gartland type III extension fractures, and 111 were treated via primary closed reduction and percutaneous smooth Kirschner wire pinning, of which 82 were followed up for an average of 3.5 years and were studied in detail clinically and radiologically. There were two cases of superficial pin tract infection and one of ulnar nerve palsy associated with the pinning. Nineteen fractures (10.5%) had an initial nerve palsy related to the injury. All recovered completely from 4 weeks to 40 weeks postinjury. Only one of nine cases (5%) with absent radial pulse required exploration. Eighty percent of all cases had excellent or good function according to the Flynn criteria of elbow assessment. The most important factor correlating with the final varus deformity was found to be the difference in Baumann's angle between the injured and the normal side after closed reduction and pin fixation. The results of cross pinning in eight cases were not found to be different from those of the lateral pinning group (74 cases). Ipsilateral fracture of the same limb occurred in 4.4% of the cases, the majority being a fracture of the distal radius. The average anesthetic time for the procedure was 54 min, and the average hospital stay was 2.9 days. Our study shows that cross or lateral percutaneous pinning was found to be effective in the treatment of Gartland type III extension fractures with a high success rate and minimal complications.