As a new screening procedure, intraoperative ultrasonography using high-resolution real-time instruments was used routinely in 84 colorectal cancer operations to scan the entire liver for liver metastases. In 10 operations (11.9%), intraoperative ultrasonography identified 14 previously unrecognized metastatic tumors, all of which were less than 2 cm in size and were nonpalpable. The sensitivity of this technique in detecting metastatic liver lesions (97.8%) was significantly superior (p < 0.01) to that of preoperative ultrasound (41.3%), computed tomography (47.8%), and surgical exploration (58.7%), while the specificity of each test was comparable (approximately 90%). High-resolution intraoperative ultrasonography is safe, simple to perform and more accurate than preoperative imaging and surgical exploratory methods. Therefore its use is encouraged during colorectal cancer surgery for screening of liver metastases.