To evaluate the relationship between cervical intraepithelial neoplasia (CIN) and undernutrition, a pair-matched case-control study was conducted in a low-income urban population. As a broad measure of nutritional status, serum albumin, serum ferritin, hematocrit, percent desirable weight, and percent calories consumed as protein were examined. Cases (n = 102) had biopsy-confirmed CIN I, II, or III, and clinic controls (n = 102), matched on age, race, and clinic, had normal Pap smears. Survey-collected data and frozen serum were utilized to study the hypothesized association. Crude and adjusted odds ratios and 95% confidence intervals were estimated using conditional logistic regressions. Results suggest a protective role for serum ferritin for those in the highest quartile relative to those in the lowest quartile. Controlling for smoking and monthly personal income, an adjusted odds ratio of 0.2 with a corresponding 95% confidence interval of 0.1-0.7 was observed. Similar findings were noted when all other available CIN risk factors were controlled. In addition, a dose gradient was present for dietary iron intake (p = 0.01). No associations were observed between each of the other undernutrition indexes and CIN. Although only high levels of serum ferritin were associated with a protective effect against CIN, when coupled with the results from other studies that suggest carotenoids, folates, and vitamin C to be protective, the overall hypothesis that poor nutriture is associated with CIN remains viable. Lack of an association with the other nutritional indexes may reflect the relatively sufficient nutritional status of low-income individuals residing in the United States, as opposed to the undernourished population of the Third World.