Objective: The objective of this study was to evaluate whether mandatory fortification of grain products with folic acid in the United States is associated with changes in DNA methyltransferase-1 (Dnmt-1) expression in cells involved in cervical carcinogenesis. Methods: Archived specimens of cervical intraepithelial neoplasia (CIN) diagnosed before (1990-1992) and after (2000-2002) mandatory folic acid fortification were used to examine the expression of Dnmt-1 in specific lesions involved in cervical carcinogenesis by immunohistochemistry. The total number of lesions examined was 101 in the prefortification period and 96 in the postfortification period. Immunohistochemical staining for Dnmt-1, its assessment, and data entry were blinded with regard to the fortification status. Results: Age- and race-adjusted mean percentage of cells positive for Dnmt-1 or the Dnmt-1 score was significantly higher in all lesion types (i.e., normal cervical epithelium, reactive cervical epithelium, metaplastic cervical epithelium, CIN, or carcinoma in situ) detected in the postfortification period compared with the prefortification period (P < 0.05, all comparisons). The degree of Dnmt-1 was significantly higher (P < 0.0001) in CIN ≥2 lesions compared with CIN ≤1 lesions, regardless of the fortification group. Conclusion: These results suggest that mandatory fortification with folic acid in the United States seems to have resulted in a change in the degree of expression of Dnmt-1 in cells involved in cervical carcinogenesis. Because the approach we have taken to demonstrate these differences have limitations inherent to a study of this nature and this is the first study to report a folate fortification associated change in Dnmt-1, validating these results in other study populations and/or with other techniques of assessing Dnmt-1 will increase the scientific credibility of these findings. © 2008 Elsevier Inc. All rights reserved.