The incidence of synchronous and metachronous liver metastases in patients with colorectal cancer is extremely high. Approximately 25 per cent of patients will have overt liver metastases at the time of presentation, and in the remainder up to 40 per cent will eventually develop liver metastases. In an attempt to obtain a prognostic index for the prediction of those patients most likely to develop liver metastases, 134 patients with primary colorectal cancer but without overt liver metastases at initial presentation were followed up for between 5-10 years. Regular liver scans were performed and the presence of liver metastases observed. A total of 47 patients developed liver metastases. Those preoperative variables related to the subsequent development of liver metastases were sex, log10 serum alkaline phosphatase level and Dukes' classification. A prognostic index using these parameters has been calculated.