Ten patients undergoing major abdominal surgery under general anaesthesia were monitored with a pulse oximeter, electroencephalogram, electromyogram, electrocardiogram and eye and hand movement sensors two nights before and three nights after surgery. Episodic hypoxaemic events were increased significantly after surgery (P<0.05). Rapid eye movement (REM) sleep decreased significantly on the first night after operation (P < 0.05). Seven patients had increased amounts of REM sleep (rebound) on the second, third or both nights after operation compared with the preoperative night. Slow wave sleep was depressed significantly on the first two nights after operation (P < 0.05). REM sleep-associated hypoxaemic episodes for individual patients increased about three-fold on the second and third nights after operation compared with the night before operation (P < 0.05). We conclude that postoperative sleep pattern is disturbed severely with early depression of REM and slow wave sleep and with rebound of REM sleep on the second and third nights. Postoperative rebound of REM sleep may contribute to the development of sleep disordered breathing and nocturnal episodic hypoxaemia.