We investigated the value of ultrafast computed tomography for the preoperative assessment of colorectal carcinoma. Ultrafast CT demonstrated the primary tumor in 25 (89%) of 28 patients. Local tumor extension was detected with a sensitivity of 90%, a specificity of 78%, and an overall accuracy of 82%. Invasion into adjacent organs was detected with a sensitivity of 80%, a specificity of 91%, and an overall accuracy of 89%. Diagnoses of pericolic or perirectal lymph node metastasis were true-positive in ten, true-negative in 12, false-positive in one, and false-negative in two and those for distant lymph node metastasis were true-positive in four, true-negative in 24, and false-negative in one. Ultrafast CT may be more useful than conventional CT in evaluating local extension and pericolic or perirectal lymph node metastases because it avoids motion artifact.