Calcium/calmodulin-dependent serine protein kinase (CASK), which localizes at cell-cell adhesion sites and binds to the heparan sulfate proteoglycan syndecan-2, is involved in cell proliferation, cytoskeletal remodeling, and cell migration. To demonstrate the role of CASK in colorectal cancer (CRC) carcinogenesis, we examined the expression of CASK and its binding protein syndecan-2 in human CRC tissues. The expression of CASK was measured in CRC specimens and the controls from adenomas and normal mucosae by immunohistochemical staining and Western blot analysis. Syndecan-2 protein level was tested in CRC samples and the controls by Western blot analysis. The correlations between CASK expression and clinicopathological variables, including disease-free survival (DFS) and overall survival (OS), were analyzed. Compared to the controls, both CASK and syndecan-2 expression were enhanced in CRC tissues. Furthermore, high expression of CASK and syndecan-2 was significantly correlated with advanced tumor stage, lymphatic invasion, lymph node metastasis, vascular invasion, liver metastasis, and unresectable metastatic CRC. Survival analysis showed that patients with low CASK staining had a significantly better survival compared to patients with high CASK staining. In multivariate analysis, CASK overexpression, advanced tumor stage, lymph node metastasis, vasvular invasion, and liver metastasis were independent prognostic factors of poor DFS and OS. Our present study indicates that CASK overexpression is associated with an unfavorable prognosis. CASK is an independent prognostic factor for CRC, which suggests that it is a novel and crucial predictor for CRC metastasis.