Introduction:Several genes determine the development of colorectal cancer (CRC), such as MLH1, which encodes a protein that participates in DNA repair. MLH1 hypermethylation has been associated with gene silencing. Objective: To analyze the methylation of five regions of MLH1 CpG island in colorectal tumors from Mexican patients. Materials and methods: One hundred and one tumor tissue samples were obtained from Mexican patients with CRC who provided informed consent. DNA was subjected to bisulfite conversion. Methylation of all five regions of the CpG island was evaluated using methylation-specific PCR. Results: The frequency of methylation in Mexican patients with CRC was 25%. Regions A and B methylation was the main observed pattern (60%). Female patients showed a higher frequency of methylation (71%; OR: 3.085; CI: 1.85-8.03; p = 0.02), and out of total methylated samples, 80% corresponded to individuals older than 45 years (p < 0.05). Conclusion: We calculated a methylation frequency for the MLH1 gene of 25% in Mexican patients with CRC, with this being the first report for this population. Female patients and patients older than 45 years showed a higher frequency of methylation.

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