Enlargement of the calf usually is associated with venous thrombosis, haemorrhage, focal myositis or a tumour in bone or muscle. Occasionally a calf enlargement is due to isolated muscle hypertrophy as a sign of radicular or peripheral nerve injury. Most neurogenic muscle hypertrophy is confined to the calf muscle, but the phenomenon has also been seen in other muscles. Three patients with S-I radiculopathy leading to ipsilateral neurogenic calf hypertrophy following hernia nuclei pulposi are described, two men of 79 and 78 years old and a woman of 46 years. The symptoms gradually subsided with time and conservative treatment. The pathogenesis of neurogenic muscle hypertrophy possibly involves partial denervation atrophy and compensatory hypertrophy of remaining muscle fibres.