© 2014 © The Author 2014. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: firstname.lastname@example.org. The Western dietary pattern is associated with higher risk of colorectal neoplasms. Evolutionary discordance could explain this association. We investigated associations of scores for 2 proposed diet patterns, the "Paleolithic" and the Mediterranean, with incident, sporadic colorectal adenomas in a case-control study of colorectal polyps conducted in Minnesota (1991-1994). Persons with no prior history of colorectal neoplasms completed comprehensive questionnaires prior to elective, outpatient endoscopy; of these individuals, 564 were identified as cases and 1,202 as endoscopy-negative controls. An additional group of community controls frequency-matched on age and sex (n = 535) was also recruited. Both diet scores were calculated for each participant and categorized into quintiles, and associations were estimated using unconditional logistic regression. The multivariable-adjusted odds ratios comparing persons in the highest quintiles of the Paleolithic and Mediterranean diet scores relative to the lowest quintiles were, respectively, 0.71 (95% confidence interval (CI): 0.50, 1.02; Ptrend = 0.02) and 0.74 (95% CI: 0.54, 1.03; Ptrend = 0.05) when comparing cases with endoscopy-negative controls and 0.84 (95% CI: 0.56, 1.26; Ptrend = 0.14) and 0.77 (95% CI: 0.53, 1.11; Ptrend = 0.13) when comparing cases with community controls. These findings suggest that greater adherence to the Paleolithic diet pattern and greater adherence to the Mediterranean diet pattern may be similarly associated with lower risk of incident, sporadic colorectal adenomas.