Thirty-three hands were followed for an average of 7.8 years after arthroplasty of the basal joint of the thumb using a silicone prosthesis. The minimum length of follow-up was 5.6 years. All of the patients had relief of pain, but three complained of weakness. Radiographs of twenty hands showed that four prostheses had subluxated, three had dislocated, and thirteen had evidence of wear. Ten hands had destructive changes in the adjacent bones. We now recommend the use of a silicone prosthesis for arthroplasty of the basal joint only in elderly patients or in patients who have a low level of functional activity. In younger or more active patients, interpositional arthroplasty using tendon is recommended.