Muscle hypertrophy is rare in denervating diseases. A patient with calf enlargement associated with L5-S1 radiculopathy and another with thenar, hypothenar, forearm and calf muscle hypertrophy in the course of chronic relapsing inflammatory demyelinating polyneuropathy are described. Gastrocnemius muscle biopsy revealed both type I and type II fibre hypertrophy in the former case and predominant type I fibre hypertrophy in the latter. Passive stretching and abnormal spontaneous muscular activity might have played a role in the origin of hypertrophy in both patients, but a satisfactory explanation for denervation hypertrophy has yet to be provided.