Gastric cancer is more than twice as common in Hispanics as in Anglos in Texas, while colorectal cancer is almost twice as common in Anglos as Hispanics. To test the hypothesis that mutations in the p53 tumour suppressor gene are involved in these differences, we examined 131 gastric and 138 colorectal cancers from Hispanic and Anglo patients from South Texas and Mexico using immunohistochemistry (IHC) as a screening assay for p53 mutations. The fraction of p53 positive cases was not significantly different in gastric cancers from Hispanics compared to Anglos (43% versus 61%, respectively, p = 0.13) or in colorectal cancer (57% versus 58%, respectively, p = 1.0), suggesting that p53 mutations are not involved in causing the different incidences of these cancers in these populations. In addition, the types of p53 mutations arising in gastric tumours from Hispanic patients were consistent with those reported in gastric tumours in other populations. Sequencing of mutations in five gastric cancers revealed two G:C to A:T transitions, two A:T to G:C transitions and one complex deletion. In contrast with findings in studies in other tumour types, neither stage nor survival was associated with p53 positive staining by IHC in either gastric or colorectal tumours in this study. Positive p53 immunostaining was associated with the diffuse histological subtype in gastric carcinoma (p = 0.05) and high histological grade in colorectal carcinoma (p = 0.04).