AIM: To investigate the causal relationship between hypoadiponectinemia and colorectal carcinogenesis in in vivo experimental model, and to determine the con-tribution of adiponectin deficiency to colorectal cancer development and proliferation. rnMETHODS: We examined the influence of adiponectin deficiency on colorectal carcinogenesis induced by the administration of azoxymethane (AOM) (7.5 mg/kg, in-traperitoneal injection once a week for 8 wk), by using adiponectin-knockout (KO) mice. RESULTS: At 53 wk after the first AOM treatment, KOmice developed larger and histologically more progres-sive colorectal tumors with greater frequency com-pared with wild-type (WT) mice, although the tumor incidence was not different between WT and KO mice. KO mice showed increased cell proliferation of colorec-tal tumor cells, which correlated with the expression levels of cyclooxygenase-2 (COX-2) in the colorectal tumors. In addition, KO mice showed higher incidence and frequency of liver tumors after AOI treatment. Thirteen percent of WT mice developed liver tumors, and these WT mice had only a single tumor. In contrast, 50% of K.O mice developed liver tumors, and 58% of these KO mice had multiple tumors. rnCONCLUSION: Adiponectin deficiency enhances colorectal carcinogenesis and liver tumor formation induced by AOM in mice. This study strongly suggests that hypoadiponectinemia could be involved in the pathogenesis for colorectal cancer and liver tumor in human subjects.