This study was performed to determine whether the adoption of a standardized technique for resection of colon cancer, based on mobilization along anatomic planes, resulted in improved survival after adjustment for other known prognostic factors. Patients undergoing a potentially curative, elective colonic resection at Concord Hospital from 1971 to 1995 were included. None received adjuvant therapy. Data were recorded prospectively. Overall survival and colon-cancer-specific survival were examined by the Kaplan-Meier method and proportional-hazards regression in relation to patient and tumor characteristics and the introduction of a standardized surgical technique in 1980. Overall five-year survival rose from 48.1 percent before 1980 to 63.7 percent after 1980 (P < 0.0001); cancer-specific survival rose from 66.4 percent to 76.6 percent (P = 0.002). Factors that did not change significantly before and after 1980 were patient age and gender, tumor site, stage, grade, serosal surface involvement, and apical node metastases. The proportion of tumors > or =5 cm in diameter decreased after 1980 (61.9 to 49.2 percent, P = 0.001) but survival was unrelated to size. Venous invasion rose after 1980 (9 to 15.8 percent, P = 0.014). Multiple regression with adjustment for age, stage, grade, venous invasion, serosal surface involvement, and apical node metastases showed significantly shorter overall survival before the introduction of the standardized technique (hazard ratio, 1.5; 95 percent confidence interval, 1.2-1.8) and significantly shorter colon-cancer-specific survival (hazard ratio, 1.7; 95 percent confidence interval, 1.3-2.2). The proportion of patients having a noncurative operation because of residual tumor in a line of resection (excluded from the survival analyses) fell from 10.6 percent (confidence interval, 7-15.3 percent) before 1980 to 3.2 percent (confidence interval, 2-4.9 percent) after 1980. As in rectal cancer surgery, mobilization of the colon along anatomic planes is an important principle that influences outcome and needs to be emphasized.