A prospective investigation of 188 patients with cancer of the rectum and rectosigmoid colon with synchronous liver metastases is described. The mean survival time for 183 patients who did not receive any treatment for the liver metastases was six months and only one survived for longer than 37 months. After extirpation of the primary tumour, the most significant prognostic factors were etrahepatic metastases, enlarged liver on account of metastases and more than three liver metastases. Serum basic phosphatases had the greatest significance among a series of laboratory tests. In the sub-groups with the best possible prognoses, the mean survival time was 12 months. 25% five-year survival has been described in the literature following resection of the liver in patients with a maximum of three metastases, no other metastases and age under 70 years. Provided this holds true, liver surgery will be a therapeutic possibility in at least 100 patients per annum in Denmark with synchronous liver metastases and 25 of these will be cured. This figure requires an improved programme for the diagnosis of synchronous liver metastases than at present and the same high frequency of extirpation of the primary colorectal cancer on a national basis which was achieved in the present material.