Diabetes mellitus (DM) is occasionally associated with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) raising the question of coexistence or etiological link. The study compares, neurophysiological and outcome of CIDP patients with and without DM. Consecutive CIDP patients were subjected to detailed clinical evaluation, haematology, serum chemistry, vasculitis profile, paraproteins, myeloma screening and cerebrospinal fluid (CSF) examination. Electrodiagnostic (EDx) tests included motor and sensory conduction and F-wave studies. The patients were treated with oral prednisolone 1 mg/kg/day with or without azathioprine 1-2 mg/kg and followed up for 6 months. The clinical and EDx finding in CIDP with and without DM were compared. Thirty-five CIDP patients were included and nine had DM. CIDP with diabetes (CIDP-D) had higher frequency of autonomic dysfunction. In CIDP-D, motor (38.9% vs. 16.7%) and sensory (40.7% vs. 14.1%) nerve conductions were more frequently unrecordable or had reduced compound muscle action potential (CMAP) amplitude. F-waves were also more frequently unrecordable in CIDP-D (28.8% vs. 12.8%) compared with idiopathic CIDP (I-CIDP). The degree of conduction block was more in I-CIDP. At 6-month follow up, I-CIDP patients improved better than CIDP-D. CIDP-D patients present with higher frequency of autonomic dysfunction, electrophysiological evidences of associated axonal loss and had a poorer outcome at 6 months compared with I-CIDP.