Pain in the postoperative period has remained a clinical problem in spite of major progress in pain assessment and management. The aim of the present study was to describe in detail the time course of pain experiences of surgical patients (n=200) following elective surgical procedures. Visual analogue scale (VAS, 0-100 mm) was used for pain intensity ratings at 4, 24, 48, and 72 hours after surgery. Interviews were carried out to assess the occurrence of intermittent worst pain episodes during each 24-hour period and to relate such experiences to clinical events. At 4, 24, 48, and 72 hours postoperatively, 39%, 43%, 27%, and 16% of the patients, respectively, experienced moderate or even severe pain (VAS > or =40 mm) at rest. During the first 24 hours after surgery, 88% of the patients had experienced moderate or severe pain at some time (VAS > or =40 mm). Corresponding figures for the following 24 hour periods were 81% and 72%, respectively. Spontaneous pain breakthrough and movement/mobilization were identified as reasons for the worst pain episodes during the first 72-hour period after surgery. The probability of pain intensity of VAS >40 mm was calculated from individual regression functions. The probability was found to be much higher for patients receiving parenteral analgesics than for patients receiving prolonged epidural analgesia. Despite major improvements in pain assessment and management, postoperative patients often experience moderate to severe pain, and worst pain episodes occur even in the late postoperative phase. The present study emphasizes that in the clinical routine management of pain, further quality assurance efforts are necessary.