This study assessed the utility of document prevalence and familiarity as predictors of adult document literacy performance. Three indexes--quantifying document prevalence, document familiarity, and the frequency of document use--were constructed using survey responses from an adult community sample and documents collected from government agencies and businesses. All three indexes significantly predicted document task performance on the 1992 National Adult Literacy Survey and the 2003 National Assessment of Adult Literacy, both of which were administered by the U.S. Department of Education. The three indexes, as individual predictors, accounted for 70% (familiarity), 51% (frequency of use), and 31% (prevalence) of the variation in document task performance. Document familiarity may aid in the search and retrieval of information from documents, thereby facilitating document literacy. (Contains 2 tables, 4 figures and 1 note.)