We report the clinical and EMG details of 67 consecutive patients with strictly defined chronic inflammatory demyelinating polyneuropathy (CIDP) during a 4-year period and compare responses to treatment in patients with idiopathic CIDP (CIDP-I) and CIDP with monoclonal gammopathy of uncertain significance (CIDP-MGUS). Patients were examined an average of 28 months after first symptoms. There were several variant presentations that still conformed to the clinical and electrophysiologic definitions of CIDP, including a pure motor syndrome (10%), sensory ataxic variant (12%), mononeuritis multiplex pattern (9%), paraparetic pattern (4%), and relapsing acute Guillain-Barré syndrome (16%). Pain was more frequent than in previous studies (42%). Conduction block was the commonest EMG abnormality (detected in at least one nerve in 73% of patients), but only 31% had a pure demyelinating neuropathy and the majority had some degree of axonal change. Patients with CIDP-MGUS had less severe weakness, greater imbalance, leg ataxia, vibration loss in the hands, and absent median and ulnar sensory potentials, but were as likely as CIDP-I patients to respond to plasma exchange. Seventeen of 44 patients (39%) with idiopathic CIDP improved for at least 2 months with an initial therapy. Although the response rates among plasma exchange, IVIG, and steroids were similar, functional improvement (Rankin score) was greatest with plasma exchange. Of 26 patients who failed to respond to an initial therapy, 9 (35%) benefited from an alternative treatment, and of the 11 who required a third modality 3 (27%) improved. Overall, 66% responded to one of the three main therapies for CIDP.