Carpal tunnel release (CTR) is regarded as a common and successful operative procedure in hand surgery. However, an increasing number of patients with complications have been referred to our hospital. This retrospective investigation was undertaken to clarify the reasons for persisting or recurrent symptoms in 200 patients who underwent secondary exploration during a 26 month period at a single institution. In 108 cases, the flexor retinaculum was found to have been released incompletely. In 12 patients, a nerve laceration had occurred during the primary intervention. In 46 patients, symptoms were due to the nerve being tethered in scar tissue. The re-exploration revealed circumferential fibrosis around and within the median nerve in 17 patients and a tumour in the carpal tunnel in four patients. In 13 patients, no specific reason was found for recurrence of symptoms. We conclude that CTR seems to be a widely underestimated procedure and revision surgery could be largely avoided by reducing technical errors during the primary operation.