Wnt signal pathway is involved in the pathogenesis of multiple cancer types. Moreover, upregulation of downstream transcription factors, such as TCF/LEF family, is proved in several of them. One of this neoplasms is stomach cancer, which is, according to Laurén classification histologically divided into three categories: intestinal, diffuse and mixed type. Stomach cancer is nearly at the top of the list of leading causes of death from malignant diseases worldwide, and many studies search for new treatment possibilities which would improve survival and quality of life of patients suffering from this disease. The aim of this study was to prove that there is a difference in expression of TCF1 protein between normal tissue and diffuse stomach cancer, with the assumption that this protein may have a role in the pathogenesis of this type of stomach cancer. 36 samples of diffuse gastric carcinoma and 43 samples of normal stomach tissue gathered at the Clinical Institute of Pathology and Cytology of the Zagreb University Hospital Centre were analyzed. After the use of immunohistochemical staining, stereological quantitative analysis was done and a statistically significant difference (p< 0,05) in expression of TCF1 protein between healthy tissue cells and the cells of diffuse gastric carcinoma was found. With this result we concluded that this part of the Wnt signaling pathway could have a role in the pathogenesis of diffuse gastric carcinoma. Further studies are needed to explore the role of TCF1 protein and its potential use in new therapic procedures.