To study the incidence of pain upon injection of 1% propofol (Propofol-Lipuro 1%, B. Braun, Melsungen, Germany) in a 10% fat emulsion containing equal proportions (50:50) of medium- and long-chain triglycerides.The subjects were 600 adult patients scheduled for elective surgery. The use of premedication was left to the discretion of the anesthesiologist. All patients received the study anesthetic injected slowly (20-40 mg per 10 seconds) at a dose of 1.5 to 2.5 mg/Kg. Variables recorded were incidence and type of pain upon administering the anesthetic, the patients' clinical characteristics, premedication administered, and method of venous puncture. Bivariate and multivariate statistical analyses were performed to determine factors associated with the appearance of pain.The overall incidence of pain upon administration of propofol-lipuro was 27%. Pain was moderate to intense in 9%. Premedication did not affect the incidence of pain with injection. The risk factors that predicted the appearance of pain were injection through a small-caliber catheter (> 18 G) and injection on the dorsal hand (P < 0.05).The incidence of pain upon injection of propofol-lipuro is low in comparison with incidence rates reported in the literature for the traditional formula, but administration of the fat emulsion formula through a vein on the dorsal side of the hand or through a venous catheter smaller than 18 G should be avoided. Double-blind randomized controlled trials should be conducted to clarify the advantages that propofol-lipuro seems to offer.