Objectives <p>This study aimed to, first, determine the prevalence of periodontitis in patients diagnosed with colorectal cancer (CRC) through a comprehensive clinical periodontal evaluation, and second, to analyze the relationship between periodontitis and different tumor severity variables.</p> Materials and methods <p>In a cross-sectional and analytical study in patients with CRC, we divided the patients into two groups, periodontitis and non-periodontitis, based on a complete periodontal assessment (clinical attachment loss, probing pocket depth, bleeding on probing, plaque index, number of present teeth, and a periodontal severity index). In both groups, in addition to sociodemographic variables, 12 histopathological tumor severity variables were compared.</p> Results <p>Out of 59 patients diagnosed with CRC, 41 (69.5%, 95% CI: 56.1–80.8) were diagnosed with periodontitis. The mean values in ng/mL of baseline and peak carcinoembryonic antigen (CEA) in the periodontitis patient group, mean ± SD (0.44 ± 0.39, 0.69 ± 0.49), were much higher compared to the non-periodontitis group (0.11 ± 0.29, 0.35 ± 0.45), 95% CI: 0.12–0.54, <i>p</i> &lt; 0.001 and 95% CI: 0.06–0.62, <i>p</i> = 0.005, respectively. The rest of the comparisons between the different characteristics and histopathological variables of the tumor showed very similar results between both groups.</p> Conclusions <p>The 69.5% prevalence of periodontitis in patients with colorectal cancer highlights the relationship between both diseases. Furthermore, the association between periodontitis and elevated CEA levels suggests a possible role of chronic inflammation in tumor susceptibility. However, the absence of an association with other histopathological variables suggests that periodontitis is not related to cancer severity.</p> Clinical relevance <p>Recognizing periodontitis as a potential field cancerization highlights the importance of periodontal management as a possible strategy to reduce CRC susceptibility.</p>