A 79-year-old man who, after scheduled laparoscopic cholecystectomy converted due to anatomical difficulties, presented on the first postoperative day with an external biliary fistula due to environmental drainage. In the imaging tests performed, some of which were repeated twice (ultrasound, CT, CT with pigtail drainage of the biloma, cRMN, diagnostic ERCP and subsequent ERCP with placement of a 7 cm 10 F biliary stent), the cause of the persistent biliary fistula could not be demonstrated, presenting the integrity of the intra- and extrahepatic biliary tract, with anatomical and functional characteristics of normal appearance. The debit of the external biliary fistula, however, ranged between 200 and 400 cc. daily. Laboratory tests showed an alanine aminotransferase of 109 U/l (7-40 U/l); aspartate aminotransferase of 98 U/l (7-40 U/l); GGT of 120 U/l (7-40 U/l); alkaline phosphatase of 262 U/l (7-40 U/l); total bilirubin of 1.8 mg/dl (0.2-1.3 mg/dl). Despite the internal biliary drainage of the main bile duct, the persistence of the external biliary fistula led to the suspicion of an aberrant duct, so it was decided to operate 45 days after the initial cholecystectomy, requesting our intraoperative collaboration due to the difficulties encountered in the identification and interpretation of the findings of the operative field in the biliary hilum. Only intraoperatively did cholangiography through the mouthpiece of the juxtahilar biliary fistula show that the lesion originated in an aberrant duct of the independent right anterior sector (segments V-VIII), without any relation to the rest of the intrahepatic biliary tree, confirming the diagnostic suspicion and making it possible to treat the lesion by means of a Roux-en-Y loop cholangiojejunostomy with transanastomotic guidance by means of a siliconised paediatric feeding catheter. On the 7th postoperative day a transcatheter cholangiography was performed with absolute normality of the anastomosis and absence of leaks, and the patient was discharged. The transanastomotic tutor was removed one month after surgery after a second cholangiographic control, demonstrating the total integrity and functionality of the anastomosis. In the annual controls the patient maintains a total normality of the analytical tests.