The additional value of laparoscopic ultrasonography was evaluated prospectively in 35 patients undergoing diagnostic laparoscopy for a suspected potentially resectable proximal bile duct tumor. Findings were compared with transabdominal ultrasonography, laparoscopy, surgery, and pathology. Laparoscopic ultrasonography was able to visualize the presence and origin of small bile duct tumors or stones and small liver metastases, which could not be seen or could be visualized only doubtfully by ultrasonography and laparoscopy. Laparoscopic ultrasonography was more useful in staging of small tumors of the gallbladder or proximal common bile duct than in staging bifurcation (Klatskin) tumors. Additional information provided by laparoscopic ultrasonography led to a change in diagnosis or tumor stage in eight patients (23%) and to avoidance of laparotomy in three patients (9%).