Two types of gastric adenocarcinoma can be distinguished histopathologically: the diffuse and the intestinal type. Molecular pathology supports this theory by showing differences in the genetic pathways of both tumor types. In addition to known pathomorphological factors of prognosis, e.g., depth of tumor infiltration, number of lymph node metastases and resection margins, a few genes have been suggested to have prognostic impact in gastric carcinoma. Clinically relevant molecules whose expression or structure is altered include the plasminogen activator (uPA) and its inhibitor PAI-1 (plasminogen activator inhibitor type 1), the cell cycle regulator cyclin E, epidermal growth factor (EGF), the apoptosis inhibitor bcl-2, the cell adhesion molecule E-cadherin, and the multifunctional protein beta-catenin. Gene amplification and protein overexpression of the growth factor receptors c-erbB-2 and K-sam may be prognostic factors for intestinal-type and diffuse-type gastric cancer, respectively. In addition, genetic instability is commonly seen. There has long been evidence for a genetic predisposition to gastric cancer by epidemiological studies and case reports. Very recently, germ line mutations of E-cadherin have been identified that are responsible for a dominantly inherited form of diffuse-type gastric cancer and could be used to identify individuals that are at high risk.