Hematogenous metastases from primary colon or rectal cancer develop in a definite step-wise fashion. In most patients the primary tumor disseminates to local lymph nodes, to the liver, or to peritoneal surfaces. Lung metastases only develop after considerable progression of the secondary tumor deposits in liver or in lymph nodes. This is considered a metachronous or step-wise progression of the malignant process. Only in a minority of patients is there synchronous spread of the malignancy from the primary site to systemic sites. The dissemination of colorectal malignancy is in great contrast to the dissemination of other malignancies such as breast cancer or melanoma. Considerable autopsy and laboratory data support the metachronous pattern of dissemination. Metastatic inefficiency (overt destruction of a majority of tumor cells within blood vessels or lymphatic channels) explains the preponderance of metastatic deposits in the first capillary bed or first lymphatic network draining a primary colorectal malignancy. These observations constitute the scientific basis for resection of liver metastases from colorectal cancer and the large proportion of patients who can be cured by the surgical resection of one or a few liver metastases.