MRI was performed on the spinal roots, brachial and lumbar plexuses of 14 patients with chronic inflammatory demyelinating polyneuropathy (CIDP). Hypertrophy of cervical roots and brachial plexus was demonstrated in eight cases, six of whom also had hypertrophy of the lumbar plexus. Of 11 patients who received gadolinium, five of six cases with hypertrophy and one of five without hypertrophy demonstrated enhancement. All patients with hypertrophy had a relapsing-remitting course and a significantly longer disease duration. Gross onion-bulb formations were seen in a biopsy of nerve from the brachial plexus in one case with clinically evident nodular hypertrophy. We conclude that spinal root and plexus hypertrophy may be seen on MRI, particularly in cases of CIDP of long duration, and gadolinium enhancement may be present in active disease.