Objective To study the incidence，clinicopathological characteristics,diagnosis，treatment， and prognosis of synchronous or metachronous primary cancers in patients with gastric cancer． Methods The clinical data of 103 gastric cancer patients with synchronous or metachronous primary cancers from January 1983 to December 2010 were collected and reviewed．Results The incidence of synchronous or metachronous primary cancer in addition to gastric cancer was 2.26％（103/4 552）.The age of these patients was （63.98±11.93） years （30～84 years） when gastric cancer was diagnosed.There were 29 cases of synchronous primary cancer and 74 cases of metachronous primary cancer,in which there were 46 pre-metachronous cancer patients and 28 post-metachronous cancer patients.All the patients had 113 primary tumors of other organs.Colorectal cancer was the most common type of primary cancer in other organs （27.43%, 31/113）,followed by lung cancer （15.04%, 17/113）.The time interval between gastric cancer and metachronous primary cancer was （87.95±92.98） months （7～506 months）,and 65.49% （74/113） of other primary tumors were diagnosed within 5 years before or after gastric cancer. The overall 5-year survival rate was 48.43%. The 5-year survival rate of post-metachronous group （69.52%） was significantly better than synchronous cancer group （36.40%, P=0.009） or pre-metachronous group （42.31%, P=0.023）.In 33 patients who had definite cause of death, 20 patients died of gastric cancer.Conclusions Primary cancer of other organs should be considered in treatment of gastric cancer.Gastric cancer may be the most important factor impacting the prognosis of these patients.