This study was undertaken to define the factors causally related to the improvement in survival rates from colorectal cancers which have accrued in recent decades. The data indicate that the higher survival rates of recent years among individuals ill of carcinoma of the colon and rectum are attributable to improved surgical therapy. Improvements in operative mortality, operability, and resectability are responsible. Material Patients treated for carcinoma of the colon and rectum in the Barnes Hospital, St. Louis, between 1914-1951 and in the Ellis Fischel State Cancer Hospital, Columbia, Mo, between 1939-1961 constitute the population sample. The surgical practices are similar in these institutions due to frequent interchange of personnel at the staff and resident levels. Tissue sections from patients seen before 1940 at the Barnes Hospital and of all individuals treated at the Ellis Fischel State Cancer Hospital were reexamined to verify the presence of invasive cancer. Patients were excluded