Objective: to investigate the morphological and immunohistochemical features of severe gastric dysplasia (SGD) and early gastric cancer (EGC). Material and methods. The fragments of gastric tumor tissue with adjacent mucosal portions from 50 patients aged from 34 to 79 years (mean age 63.8 years), which had been removed during organ-sparing endoscopic surgery, were histologically, histochemical, and immunohistochemically (IHC) examined. Results. In EGC, there was a preponderance of intestinal-type cancer; the adjacent mucosal areas showed foci of SGD and colonic metaplasia in 100%. Cancer emboli were absent in the lumen of blood and lymphatic vessels in EGC at a рТ1а stage. Relapse of cancer occurred in 10% of the patients with EGC within 6-24 months after endoscopic dissection. Conclusion. Complex morphological and IHC examination allows timely diagnosis of SGD and EGC, namely: the ability to assess the histologic type and depth of invasion of EGC, the presence or absence of cancer emboli in the blood and lymphatic vessels, which is crucial in determining treatment policy and prognosis. The immunophenotype of SGD and EGC with a number of antibodies (Abs) (cytokeratins 7, 8/18, mucins 1, 2 and 5AC, and p53) was assessed, the most significant ones of which were, in our opinion, Abs to p53 and mucin 5AC.