This is a prospective study that describes 18 patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), idiopathic type. The patients have been followed for a period of 4 to 127 months. We evaluated the clinical characteristics, the evolution, and therapeutic response. Male patients outnumbered female patients in a proportion of 1.25:1. Symptoms first appeared at an age ranging from 6 to 85. Most of the patients denied the occurrence of preceding events and a progressive evolution prevailed over relapsing evolution. All patients had both motor and sensory dysfunction associated with loss of tendon reflexes, and only three patients (16.7%) had cranial nerve involvement. The cerebrospinal fluid protein levels were increased in 88.9% of the patients and mean level was 203.4 mg/dl. Electrophysiological studies revealed demyelination in all patients and axonal damage in 94.4%. Preponderant characteristics in the sural nerve biopsy of seven patients showed demyelination and remyelination, and changes indicative of axonal damage were often present. The anti-HLA Dr antibodies were found in the sural nerve of one patient and anti-CD3 antibodies in the sural nerve of two. All patients were first treated with prednisone. The drug was maintained in reduced doses and given in alternate days to 72.2% of the patients with success. Two patients (11.1%) are asymptomatic even after the withdrawal of all medication. We administered azathioprine, associated or not with corticoid, to the four patients who had not had a satisfactory response to the prednisone treatment. By the time of the last evaluation 16 patients (88.9%) had functional improvement.