Colorectal cancer (CRC) is a heterogeneous disease that results from the accumulation of mutations in colonic mucosa cells. A subclass of CRC is characterized by microsatellite instability, which is thought to occur mainly through inactivation of the DNA mismatch repair genes MLH1 and MSH2. The inositol 5-phosphatase SHIP1 is expressed predominantly in hematopoietic cells. In this study, the expression of SHIP1 in carcinomas and its putative correlation with clinicopathologic parameters, expression of DNA repair genes and microsatellite instability was investigated. By analyzing a multi-tumor tissue microarray, expression of SHIP1 was detected in 48 out of 72 cancer entities analyzed. The expression of SHIP1 protein of 145 kDa was confirmed by Western blot analysis in 7 out of 14 carcinoma cell lines. Analysis of a large colorectal cancer tissue microarray with 1009 specimens revealed SHIP1 expression in 62% of the samples analyzed. SHIP1 expression was inversely correlated with lymph node metastasis, vascular invasion and tumor grade, and it was positively associated with left-sided tumor localization. Interestingly, a strong relationship between the expression of SHIP1 and nuclear and membranous beta-catenin and the DNA repair genes MLH1 and MSH2 was observed.