The Wnt-beta-catenin pathway plays a central role in colorectal tumorigenesis. Frizzled-related protein (FRZB, also termed secreted frizzled-related protein 3, sFRP3) antagonizes the signaling of wingless (Wnt) ligands through the frizzled membrane-bound receptors, resulting in beta-catenin destabilization thereby suppressing the expression of target genes. Recently, the FRZB Gly324 variant has been shown to have an attenuated ability to antagonize Wnt signaling and to be associated with an increased osteoarthritis risk. Here, we investigated, for the first time, the role of Arg324Gly (970C>G) along with Arg200Trp (598C>T) on colorectal cancer (CRC) risk by analyzing 659 patients and 607 control individuals drawn from the German DACHS (Darmkrebs: Chancen der Verhütung durch Screening) study. Although Arg200Trp showed no effect on CRC risk, we found homozygous carriers of Gly324 more frequent in cases than in controls, leading to a significantly increased risk for CRC [odds ratio (OR) = 5.1, 95% confidence interval (95% CI) = 1.74-14.71, P < 0.001]. The association was stronger in rectal cancer (OR = 7.52, 95% CI = 2.40-23.25, P < 0.0001) than in colon cancer (OR = 3.66, 95% CI = 1.14-11.76, P < 0.05). Since modified Wnt signaling and down-regulation of frizzled-related proteins have been observed in many human cancers, this variant may also affect the susceptibility to other cancers.