A patient with a chronic discharging sinus or an extensive adherent scar is never safe from the risk of malignant change. Examples are still occurring more than thirty years after the end of the first world war. The possibility should be kept in mind by those concerned with the long-term treatment of wounds of this kind. Reasonable prophylactic measures would be: excision of adherent or unstable scars with, if necessary, their replacement by suitable pedicle flaps having a good blood supply; and earlier amputation if a osteomyelitic sinus persists for several years and does not yield to treatment. Supervision of doubtful cases should be frequent and should not be relaxed with the passage of the years. Warty changes or indolent ulceration of scars should be regarded with grave suspicion and investigated by biopsy. Any increase in pain or discharge in association with a sinus should receive prompt attention. Finally, if malignant change supervenes, treatment should be as speedy and as radical as with any other cancer. At least thirteen of our twenty-four patients have died of cancer.