Objectives: Despite the growing number of ambulatory operations knowledge of predictive factors of postoperative pain after ambulatory surgery is limited. Therefore, the aim of this study was to identify predictive factors of postoperative pain after ambulatory surgery. Methods: In this cross-sectional study, 648 patients were included. A wide variety of elective ambulatory operations were performed. Pain assessments were made before the operation and during a 4-day period postoperatively, using a 100 mm visual analog scale. Patient characteristics, type of surgery. and type of anesthesia were recorded. In addition, preoperative expectations of postoperative pain by physician and patient were assessed. Finally, several scores about psychologic parameters were measured: pain catastrophizing, surgical anxiety, and optimism. Stepwise logistic regression analysis was performed to identify factors that independently predict the risk of having postoperative pain (defined by a visual analog scale >40 mm) oil days 0 to 4. Results: The most important predictor of postoperative pain was the presence of preoperative pain. Other predictors were anticipated postoperative pain by the clinician, preoperative high expectations of postoperative pain by the patient, younger age, and fear of short-term consequences of the operation. Regional anesthetic technique compared with general anesthesia decreased the risk of acute postoperative pain only oil the day of the operation. Discussion: Several predictive factors of postoperative pain after ambulatory surgery were identified in this study. These factors Should be taken into account when planning postoperative analgesia for ambulatory surgery.