We assessed the functional abilities of six patients who had had disarticulation of nine knees during childhood by analyzing their gait using electrocardiographic telemetry. Those who were more than five years old were further studied by timing them as they ran the fifty-yard (45.7-meter) dash and by testing the strength of the musculature of the hip girdle using a Cybex dynamometer. The physiological cost-index of Butler et al. was used to assess energy consumption. Three patients had had unilateral disarticulation and three had had bilateral disarticulation. Kinematic studies showed persistent bilateral abduction of the hip throughout the gait cycle in all six patients. The flexion-extension arc of the hip was decreased in the three who had had bilateral disarticulation. Increased flexion of the hip was noted on the normal side and decreased flexion, on the affected side in those who had had unilateral disarticulation. Phase reversal of pelvic obliquity was noted in the amputees who had had bilateral disarticulation. The prosthetic knee showed good flexion during the swing phase. All patients showed a mild decrease in the velocity of gait and in the length of step and stride. The patients who had had unilateral disarticulation showed decreased duration of the bilateral stance and single stance phases and increased duration of the swing phase. Those who had had bilateral disarticulation of the knee had a normal distribution of the components of the gait cycle: bilateral stance, single stance, and swing. The physiological cost-index for all six was within the normal range, indicating minimum energy handicap.(ABSTRACT TRUNCATED AT 250 WORDS)