Abstract: ObjectiveTo investigate the clinicopathological and diagnostic criteria of primary extragastrointestinal stromal tumor (EGIST) to provide theoretical evidence for clinicians and pathologists. MethodsThe pathologicol and clinical data of 29 cases from 1999 to 2009 which has been diagnosed with primary EGIST were analyzed retrospectively. Results In 29 cases of primary EGIST，the median age is 62 years (range from 36 to 87 years) with 13 female cases and 16 male cases. The tumors were situated in mesenterium (11 cases)，in omentum (9 cases)，in retroperitoneal (4 cases)，in pelvic (3 cases)，in crissum (1 case) and in recto-vaginal (1 case). The average size of tumors was 12.3 cm.The tumors were mainly composed of spindle cells and epithelioid cells. CD117 and CD34 are characteristically immunohistochemical markers for the diagnosis of EGIST. The most common clinical symptoms were abdomen mass and discomfort. The evaluation results of the biological behavior of the 29 primary EGIST cases were:high risk in 25 cares，medium risk in 2 cases，low risk in one patient and very low risk in one case. Conclusion sPrimary EGIST was rare and predominantly occurred in older patients. There were no differences between female and male cases. EGIST seems to occur most frequently at omentum and mesenterium and.It is rather big and often necrotize and hemorrhage grossly. EGIST also displays high potential malignancy and adverse outcome. The first choice for clinical treatment is wide excision.