This study addresses the relationship between low health literacy and comprehension of common prescription drug warning labels. Patients at an urban primary care clinic underwent structured interviews to address their understanding of specific one-step warnings (ie, take with food) and multi-step warnings (ie, avoid prolonged exposure to sunlight while taking this medication). The majority of the study population had low or marginal health literacy, defined as reading at an 8th grade level or lower. Patients with low literacy were significantly less likely to correctly interpret warning labels, and multi-step instructions were misinterpreted by the majority of respondents across all literacy levels. Misinterpretation of these common warnings could conceivably lead to misuse of medications or adverse drug events.