Patient-Controlled-Analgesia (PCA) is becoming a standard in post-operative analgesia. This prospective study was designed to get more information on the safety and the efficiency of morphine PCA following abdominal surgery. Two hundred patients were enrroled Morphine requirements, number of unsatisfied demands, patients' satisfaction and side effects were recorded for 36 hours postoperatively. The mean morphine requirement was 23.2 mg for the first 12 hours, 22.2 mg for the next 12 hours and 16 mg for the last 12 hours. Female patients required significantly less morphine than male. Interestingly such difference was no more present for patients older than 60 years. The larger the morphine bolus dose, the greater the total amount needed without any better analgesia. A bolus dose of 1 mg seemed to be the best to be recommended. The variability in the number of unsatisfied demands (i.e. demands during the lockout interval) was quite large. The number of unsatisfied demands was not influenced by the size of the bolus dose. The patients' satisfaction was high: 60% enthusiastic, 36% satisfying, 4% negative. There was no difference in satisfaction linked to gender. On the other hand, a history of a previous surgery experience without PCA raised patients' satisfaction score. Side effects were uncommon. It is concluded that morphine PCA is an efficient and safe technique of post-operative analgesia in abdominal surgery.