OBJECTIVES To evaluate patient knowledge of over-the-counter (OTC) products containing acetaminophen and to determine patients' accuracy in dosing adult, child, and infant formulations. DESIGN Cross-sectional study. SETTING Six community pharmacies in Tucson, AZ, between February and May 2011. PARTICIPANTS 88 adults aged 19 to 89 years. INTERVENTION Investigator-administered, semistructured interviews. MAIN OUTCOME MEASURES Patient knowledge of and ability to safely use OTC products containing acetaminophen, including understanding risks, identifying products, and dosing different formulations. RESULTS Although most (86%) participants heard of acetaminophen, only 68% understood at least one of its uses and only 9% knew the abbreviation APAP. Virtually all knew that consuming too much acetaminophen in 1 day could be harmful, but only 17% and 35% knew that overdoses could result in death or liver damage, respectively. On average, participants correctly identified 80% (range 27-100%) of products with and without acetaminophen from a lineup of 11 OTC products. Although 38% (n = 84) of participants correctly measured both the child and infant doses of acetaminophen, doses ranged from one-half to twice the amount of the labeled child dose and one-third of the labeled infant dose. Findings from the regression analysis suggested that on average, women and those with college degrees had higher overall scores, while participants' age or parent status were nonsignificant predictors. CONCLUSION Many patients remain confused about using acetaminophen safely, signaling the need for greater patient education to prevent unintentional harm. The results further specify common misunderstandings to address during patient contact, which also includes replacing "APAP" with "acetaminophen" on any prescription bottle labels or patient-directed information.