Abstract: The Presence of microsatellite instability (MIN)was evaluated in a series of 106 cases ofgastric cancer (GC), using radioactive PCR - based technique. MIN at one or more Loci wasobserved in 44 (41%)of the 106 GC. The relationship of MIN with Pathologic growth patterns was assessed. The results showed that the frequency of MIN was significantly higher inexpanding type of GC compared to the infiltrative type of GC(P0.005)No significant association with histologic type,pTNMstage,age or sex was found in our study(p0.05). Thesefindings indicated that MIN might be an important contributor to the pathogenesis of asignificant number of GC,especially in expanding type of GC which traditionally has a betterprognosis.