The aim of this study was to evaluate the joint count for erosions in patients with erosive osteoarthritis (EOA) of the hands treated with 800 mg/day of orally administered chondroitin sulfate plus naproxen, compared with that of patients administered naproxen only. Twenty-four consecutive patients (22 women and two men, mean age 53.0 +/- 6) suffering from symptomatic OA and with radiographic characteristics of EOA were studied. The patients were divided into two groups of 12 patients each. The first group took naproxen 500 mg/day only. The second group was treated with chondroitin sulfate 800 mg/day orally plus naproxen 500 mg/day. Radiological hand examinations were performed at baseline and again after 12 and 24 months. In both groups, the joint count for erosions showed a general tendency to increase over time. Progression of erosions at 24 months was lower in patients treated with 800 mg/day chondroitin sulfate plus naproxen than in patients taking naproxen only (p <0.05). Chondroitin sulfate failed to stop the usual time-associated progression in the number of finger joints presenting erosions in EOA of the hands. It was, however, associated with a lower increase in the number of finger joints with erosions detected after 2 years of radiological observation.