Chronic post-thoracotomy pain is a continuous dysaesthetic burning and aching in the general area of the incision that persists at least 2 months after thoracotomy. It occurs in approximately 50% of patients after thoracotomy and is usually mild or moderate. However, in 5% the pain is severe and disabling. No one technique of thoracotomy has been shown to reduce the incidence of chronic postthoracotomy pain. The most likely cause is intercostal nerve damage, although the precise mechanism for this is not known. Future work needs to examine surgical technique in detail. Until then, patients need to be adequately warned of this sequela of thoracotomy.