Gastric leiomyoblastoma is a well defined mesenchymal tumor originating from the smooth muscle tissue (tunica propria) of the body and pyloric antrum of the stomach. Although these tumors are usually benign, some of them may be malignant or potentially malignant. On gross inspection the mostly solitary lesions protrude hemispherically or polypoidly into the gastric lumen. The mucous membranes overlaying the tumor may be eroded or deeply ulcerated so that gastric hemorrhage is the most important clinical finding. Microscopically the tumor tissue is composed of large, rounded or polyhedral cells, which often contain empty vacuoles in their finely granulated acidophilic cytoplasm. The round or oval nuclei are located in the center or at the periphery of the cell, sometimes giving the impression of "signet ring" cells. The size and chromatin density of the nuclei may vary, mitotic figures are rare or missing. Often the tumor cells are disaggregated by accumulations of PAS-positive edema, which may also contain many large and confluent empty vacuoles. The reticulum stain reveals a dense network of fibers encircling individual or small groups of tumor cells, as it is characteristic for smooth muscle tissue. In 4 cases we observed small nodules, which were composed of concentrically arranged fibers and tumor cells resembling hemangiopericytoma without central blood vessel. During 6 years (1970 to 1975) we observed 6 cases of gastric leiomyoblastoma. None of these patients had evidence of recurrent disease or metastatic spread 2 to 6 1/2 years after operation and histological diagnosis of the tumor.