Breast cancer is the main cause of cancer deaths for Hispanic women. This study analyzes the role of functional health literacy on mammography screening behavior and adherence of Hispanic women. Survey data from 722 Mexican American women age 40 and over residing in the Lower Rio Grande Valley of Texas in 2008 were used to estimate logistic regression models to assess the role of functional health literacy on mammography screening behavior and adherence. About 51% of survey respondents had a functional health literacy level deemed as inadequate or marginally functional. After adjusting for other factors, women with adequate health literacy levels were more likely to report to have ever had a mammogram (odds ratio [OR] = 2.92; 95% confidence interval [CI] = 1.62-5.28), to have had a mammogram within the last 2 years (OR = 1.70; 95% CI = 1.14-2.53) or to have had one within the last year (OR = 2.30; 95% CI = 1.54-3.43), compared to women with inadequate or marginally adequate functional health literacy levels. Inadequate/marginal functional health literacy is strongly associated with lower mammography screening. Large improvements in breast cancer control in this population may come from either basic advances in health literacy or by tailored approaches to help women with low literacy navigate local health care systems.