Transdiaphragmatic pressures were measured in 3 patients with cerebellar atrophy. Recordings were made during 3 types of voluntary maneuver--maximal sniffs, full inspirations, and maximal static inspiratory efforts, and during bilateral supramaximal phrenic nerve stimulation at 1 Hz. Although diaphragmatic weakness was demonstrated during the voluntary maneuvers, transdiaphragmatic pressures recorded during phrenic nerve stimulation were normal. These findings indicate that diaphragmatic dysfunction, probably caused by ataxia during voluntary maneuvers, may occur in association with cerebellar atrophy. In the presence of diaphragmatic weakness, normal values of transdiaphragmatic pressure during phrenic nerve stimulation may suggest an upper motor neuron lesion affecting the diaphragm.