Positron emission tomography (PET) is a unique technique for imaging functional metabolism of normal and diseased tissue. Accelerated rate of glucose metabolism typical of malignant tumor cells can be detected by using fluorine-18 deoxyglucose. In this pilot study, PET FDG imaging was compared to computerized tomography for the pre-operative staging of colorectal carcinoma. We prospectively evaluated 16 patients by simultaneously performing PET FDG and CT imaging for lesions in the liver, colon and rectum. The results were compared to the operative findings in all patients. Twenty tumor sites (lymph nodes 5, colon and rectum 13, liver 2) were found on histology in 16 patients. On comparison with histology, sensitivity, specificity and predictive accuracy for detection of tumor sites were 90%, 66% and 87% with PET as compared to 60%, 100%, and 65% with CT. These findings represent increased sensitivity and predictive accuracy for staging of colorectal carcinoma with PET FDG imaging as compared to CT scanning.