In order to determine the consequences of atrophy to the cerebellar cortex on postural sensorimotor learning and performance, a natural mutation, Purkinje cell degeneration (pcd), was used. The homozygous mutants were compared to heterozygous non-ataxic controls on three static beams, two grids (vertical and tilted), a mobile beam (accelerating rotorod), and a coat-hanger. Although their posture was less stable than that of controls, the pcd mutants were not impaired in distance travelled or in latencies before falling on the static beams. Mutant performance on the grids was not impaired in comparison to controls, while a reduction of latencies before falling on the coat-hanger occurred only during the early part of training. On the accelerating rotorod, pcd mutants fell far sooner than controls and spent more time in passive rotation. By contrast to controls, pcd mutants were not able to improve with practice. Both mutants and controls were deficient during a retention test conducted 8 days after acquisition. The cerebellar cortex is critically involved in timing whole body movements during postural adjustments to a mobile beam but not to four types of immobile apparatus.