PURPOSE: A retrospective study was performed to provide an overview of changes over time by age, stage, tumor location, and surgical therapy of colorectal cancer over the past 15 years. METHODS: We analyzed the cases 6,314 colorectal cancer patients who underwent surgery at Asan Medical Center between January 1990 and December 2004. The period was divided into three periods: 1990 to 1994, 1995 to 1999, and 2000 to 2004. We analyzed trends over time for stage, resectability, and demographic factors of colorectal cancer over the past 15 years. RESULTS: The mean age of the patients in the periods from 1990 to 1994, from 1995 to 1999, and from 2000 to 2004 were 57.1 (21~89), 57.4 (14~91), and 58.9 (15~91) years, respectively, showing an increasing tendency over time (P<0.001). The male-to-female ratios were 1.2 : 1, 1.3 : 1, and 1.6 : 1, repectively, and this male preponderance has been more marked in recent years (P=0.003). There was no change in tumor location over time. The ratios of early cancer to advanced cancer were 0.06 : 1, 0.09 : 1, and 0.11 : 1, respecfively, showing an increasing tendency over time (P=0.002). The curative resection rate increased over time (P<0.001). The non-curative resection rate was higher and the non-resected rate was lower in the period 2000 to 2004 than in the period 1990 to 1999 (P<0.001). The ratios of the lowest anterior resection to the abdominoperineal resection were 0.06 : 1, 0.49 : 1, and 1.02 : 1, respectively. With decreasing tendency of abdominoperineal resection, the lowest anterior resection rate has increased gradually over time (P<0.001). CONCLUSIONS: Etiologic studies are necessary to understand the male preponderance in colorectal cancer, and multi-center studies should be conducted to understand the changing trend of colorectal cancer in Korea.