The gait of five patients with myotonic dystrophy was analyzed using light-emitting diodes and a force plate. When compared with the gait of control subjects, that of myotonics suggested weakness of the tibialis anterior and triceps surae muscles. Although the myotonics showed no evidence of lower-extremity myotonia (delayed muscle relaxation following contraction), or of weakness of the hip or knee musculature, all had striking abnormalities in their hip motion. In contrast to the smooth and consistent extension of the hip throughout stance phase observed during gait in control subjects, the hips of myotonics oscillated irregularly as they progressed through stance phase extension, with considerable variation between legs and during successive strides. Excessive use of hip musculature in an attempt to control the oscillatory hip motion may contribute to the chronic fatigue associated with myotonic dystrophy.