The objective of this study was to determine emergency department (ED) patient's understanding of common medical terms used by health care providers (HCP). Consecutive patients over 18 years of age having nonurgent conditions were recruited from the EDs of an urban and a suburban hospital between the hours of 7 a.m. and 11 p.m. Patients were asked whether six pairs of terms had the same or different meaning and scored on the number of correct answers (maximum score 6). Multiple linear regression analysis was used to assess possible relationships between test scores and age, sex, hospital site, highest education level, and predicted household income (determined from zip code). Two hundred forty-nine patients (130 men/119 women) ranging in age from 18 to 87 years old (mean = 39.4, SD = 14.9) were enrolled on the study. The mean number of correct responses was 2.8 (SD = 1.2). The percentage of patients that did not recognize analogous terms was 79% for bleeding versus hemorrhage, 78% for broken versus fractured bone, 74% for heart attack versus myocardial infarction, and 38% for stitches versus sutures. The percentage that did not recognize nonanalogous terms was 37% for diarrhea versus loose stools, and 10% for cast versus splint. Regression analysis (R2 = .13) revealed a significant positive independent relationship between test score and age (P < .024), education (P < .001), and suburban hospital site (P < .004). Predicted income had a significant relationship with test score (P < .001); however, this was no longer significant when controlled for the confounding influence of age, education and hospital site. Medical terminology is often poorly understood, especially by young, urban, poorly educated patients. Emergency health care providers should remember that even commonly used medical terminology should be carefully explained to their patients.