Objective To explore the clinicopathological features of non-familial colorectal cancer with high-frequency microsatellite instability (MSI-H). Methods One hundred and fifty patients with colorectal cancer who had no family history were enrolled in this study from June 2006 to June 2008. Five standard microsatellite loci including BAT25

BAT26

D2S123

D5S346

and D17S250 were amplified with immunofluorescent polymerase chain reaction. The patient information including age

sex

and tumor location was recorded. Pathological features including differentiation

mucinous differentiation

histological heterogeneity

and Crohn’s-like reaction were observed under light microscope. The presence of tumor-infiltrating lymphocytes (TLs

CD4+ and CD8+) was detected by means of immunohistochemistry. A regression equation was obtained by stepwise logistic regression analysis to evaluate the relationship between MSI-H phenotype in colorectal cancer ands pathological features. Results MSI-H phenotype occurred in 13.33% of the 150 patients with non-familial colorectal cancer. Poor differentiation

histological heterogeneity

Crohn’s-like reaction

and presence of TLs were found to be independent factors to identify MSI-H non-familial colorectal cancer. Logistic regression equation showed an overall sensitivity of 70.0%

specificity of 99.2%

and accuracy of 95.3% in identifying MSI-H non-familial colorectal cancer. Conclusion MSI-H non-familial colorectal cancer manifests specific pathological features

which may be relied upon for effective identification of that disease.