Carbohydrate antigen 19-9 (CA19-9) is a well-known tumor marker for pancreatobiliary cancer, and several studies have shown that an elevated serum CA19-9 level is associated with more aggressive biological behavior in gastric cancer (GC). However, the clinicopathological characteristics of CA19-9-positive GC remain unclear. We herein report an autopsy case of CA19-9-positive GC in an 84-year-old man who was admitted to our hospital because of paralysis and anemia. Autopsy revealed an ulcerative-invasive tumor measuring 72 × 60 mm in the anterior wall of the gastric body. The tumor had invaded beyond the muscularis propria, and metastasized to the lung, liver, and regional lymph nodes. Histologically, the tumor cell had oval nuclei with abundant clear cytoplasm, and tubular and/or papillary features with prominent lymphovascular permeation and perineural invasion, mimicking pancreatobiliary carcinoma. Immunohistochemically, the tumor cells showed diffuse immunopositivity for CA19-9 and carcinoembryonic antigen. According to a review of cases reported in the literature, CA19-9-positive GCs show clinicopathological characteristics such as antral location, ulcerative-infiltrating gross feature, differentiated histology, prominent lymphatic and venous invasion, higher proportion of metastasis, and higher clinical stage. These results suggest that CA19-9-positive GC is pathologically a distinctive type of tumor with aggressive biological behavior.