The purpose of this study is to clarify the correlation between cell differentiation and tumor development, including tumor aggressiveness and biological behavior. Eighty-three cases of advanced colorectal adenocarcinoma were randomly selected. Using immunohistochemical staining with antibodies to CD10, MUC2 and human gastric mucin (HGM), the colorectal adenocarcinomas could be classified into five types (18 small intestinal, 27 large intestinal, 2 gastric, 9 mixed and 27 unclassified). Each type had characteristic features. The small-intestinal type showed a relatively lower incidence of lymphatic permeation and higher venous invasion. The large-intestinal type showed a low incidence of venous invasion and lymph node metastasis. The mixed type revealed female and right-side-dominant distribution, large tumor size, high incidence of mucinous carcinoma, and low incidence of venous invasion. Gastric type was seen in only two cases (2%), which exhibited high histologic grade, lymphatic permeation and lymph node metastasis with no venous invasion. Such phenotypic classifications are considered to be useful not only for evaluation of the biological behavior of the carcinoma, but also for analysis of tumorigenesis.