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.