Multiple gastric cancers, which constitute 4% to 10% of all gastric cancers, occur in older people and are associated with more extensive intestinal metaplasia. With regard to the genesis of multiple gastric cancers, multicentricity (independent origin) rather than multifocality (local or lateral spread of one cancer) has been the favored theory. Conventional morphologic study, however, has not been able to provide convincing evidence in support of multicentricity. The purpose of this study was to verify the multicentric origin of multiple gastric cancers at a genetic level. For this purpose, immunohistochemical and molecular techniques were used to define the mutation pattern of APC, MCC and p53 in multiple lesions of synchronous multiple gastric cancers. The study was based on a total of 30 gastric tumors from 13 patients, including 10 double tumors, 2 triple tumors, and 1 quadruple tumor. Single-strand conformation polymorphism and polymerase chain reaction direct sequencing were carried out for exons 5 to 8 of p53, and loss of heterozygosity was detected on the basis of polymerase chain reaction amplification of polymorphism in exon 10 of MCC and in exon 11 of APC. Twelve of 13 cases showed alteration in one or more genetic markers. Of these, three demonstrated a discordant mutation pattern of p53 in individual lesions, and another two revealed allelic loss of MCC in one lesion and p53 mutation in the other. In six other cases, only one lesion showed alteration of APC, MCC, or p53, and in the remaining case, one lesion carried p53 and MCC mutations and the other carried MCC loss of heterozygosity only. The results of this study showed discordance of the mutation pattern of APC, MCC, and p53 in individual lesions of multiple gastric cancers, providing genetic evidence for a multicentric origin of synchronous multiple gastric carcinomas. Collectively, these findings supported the theory of field cancerization in gastric carcinogenesis.