Colorectal cancer is predominantly a disease of the elderly population, but this disease is unusual in patients 40 years of age or under, and controversy persists as to prognosis in this subset of patients. The aim of this study was to determine the clinicopathologic features and their impact on patients survival of colorectal cancer in patients aged 40 years or younger, and to compare them with those of older patients. The records of 466 patients with non-metastatic colorectal adenocarcinoma who were referred between 1991 and 1999 to the University of Istanbul, Institute of Oncology, following curative surgery were retrospectively analysed. The clinicopathologic features of 84 (18%) colorectal cancers (group A; male: female ratio 48: 36) which occurred in patients aged 40 years or younger were compared with 382 colorectal. cancers in older patients (group B; male: female ratio 194: 188). Patient gender, performance status, T stage, N stage, TNM stage, histologic grade, location of tumor, lymphatic invasion, serum levels of LDH and CEA, and survival rates were compared as prognostic factors. There was no statistically significant difference between group A and group B with respect to patient gender, performance status, T stage, N stage, TNM stage, histologic grade, location of tumor, serum levels of LDH and CEA, and survival rates of colorectal cancers. The proportion of lymphatic invasion was present in 27% of patients in group A vs. 12% in group B. With median follow-up of 69 months, the overall 5-year survival rate was 61% in group A and 56% in group B. In the univariate survival analysis according to age groups (group A and B), advanced TNM stage, location of rectal tumor, presence of lymphatic invasion, and presence of high serum LDH and CEA levels are predictors of poorer survival in young patients with colorectal. cancer. In the Cox-Regression analysis, location of tumor and TNM stage were determined as independent prognostic factors for survival. This study revealed no difference in clinicopathologic characteristics in patients with colorectal cancer aged 40 years or younger compared with those aged above 40 years. However, in patients aged 40 years or younger, distal location of tumor and advanced stage should be considered as poor prognostic factors for overall survival. (C) 2003 Tohoku University Medical Press.