On the basis of recent technological improvements, the laparoscopic approach has become the method of choice during cholecystectomy. This surgical procedure, however, needs that cholangiography be performed simultaneously to better define the anatomy of the biliary ducts and the possible presence of choledochus stones. The use of intraoperative US during cholecystectomy is nowadays advocated for the unquestionable advantages offered by this technique--i.e., its non-invasiveness, high spatial resolution and no need of contrast agent administration. In this study, we examined 30 patients with cholelithiasis who underwent laparoscopic cholecystectomy and were submitted to endolaparoscopic US besides routine intraoperative cholangiography. In all cases, both techniques allowed optimal visualization of the biliary tree, clearly demonstrating choledochus stones in 2 cases. Intraoperative US proved to be more accurate in two cases. In one case which was positive at intraoperative cholangiography, the method allowed the biliary duct filling defect to be referred to an artifact caused by the presence of an air bubble. In another case, the lack of opacification of the hepatic ducts at cholangiography was referred, after US, to extrinsic gallbladder compression. US also allowed the adjacent parenchymal organs, such as the liver and the head of pancreas, to be studied. A limitation of this technique was represented by the difficult assessment of the choledochus in the patients with anatomical abnormalities or adhesions of the intestinal loops of the upper abdomen. In conclusion, endolaparoscopic US proved to be a reliable technique in the intraoperative study of the biliary ducts and can be considered as a procedure complementary to intraoperative cholangiography.