The efficacy of intraoperative ultrasonographic detection of colorectal cancer liver metastases was evaluated in 85 patients undergoing operation for primary colorectal tumors or liver secondaries. The results of intraoperative ultrasonography were compared with those of preoperative ultrasonography and computed tomography, as well as the intraoperative appearances of the liver. Additional information about the number of metastases was obtained in 12 cases (14.1%); 17 (24.3%) out of 70 metastases could only be detected by intraoperative ultrasonography. In 4 cases (4.7%) these lesions were solitary. As a result, the operative procedure of choice was changed in 15.3% of the patients. We conclude that intraoperative ultrasonography has a significantly higher ability to detect colorectal cancer liver metastases than preoperative methods or intraoperative inspection and palpation. Intraoperative ultrasonography should be performed in patients without preoperative evidence of liver metastases and in all patients with planned resection of metastases.