Persistent or recurrent symptoms following endoscopic carpal tunnel release have been reported in 0.5% to 3% of patients undergoing this procedure. Unfortunately, preoperative risk factors for this complication have not been defined. We reviewed the records of 126 consecutive patients who underwent Agee single-portal endoscopic carpal tunnel release between June 1994 and March 1997. Five patients and six hands required subsequent open carpal tunnel release for persistent or recurrent carpal tunnel syndrome. Fulminant synovitis was identified during open carpal tunnel release in all reexplored patients, and four of the six hands were cured with open release and synovectomy. No recurrences were identified in the group of patients who presented with unilateral carpal tunnel syndrome. The presence of bilateral carpal tunnel syndrome may be a risk factor for persistent or recurrent carpal tunnel syndrome following endoscopic carpal tunnel release.