ImportanceDespite acknowledging that medical jargon should be avoided, health care practitioners frequently use it when communicating with patients.ObjectiveTo characterize the understanding of common medical jargon terms by surveying a cross section of the general public and studying phrases that have established meanings in regular usage but different meanings in a medical context (eg, negative and positive test results).Design, Setting, and ParticipantsIn this cross-sectional study, participants indicated their understanding of phrases that may have different meanings in medicine than in colloquial English via a mix of short answer and multiple choice questions. Several questions included paired phrases to assess for differences in understanding with or without jargon. Volunteers were recruited at the 2021 Minnesota State Fair near St Paul, Minnesota. An electronic survey was given to a volunteer sample of 215 adults (>18 years) who did not work or train to work in the medical field and spoke and read English.ExposuresCompleting a written or verbal survey.Main Outcomes and MeasuresThe main outcome was an accurate understanding of the medical terminology. Free-text responses were coded by 2 researchers for comprehension. Secondary outcomes looked for associations between volunteer demographics and understanding.ResultsThe 215 respondents (135 [63%] female; mean [SD] age, 42 [17] years) demonstrated a varied ability to interpret medical jargon phrases. For example, most participants (207 [96%]) knew that negative cancer screening results meant they did not have cancer, but fewer participants (143 [79%]) knew that the phrase “your tumor is progressing” was bad news, or that positive lymph nodes meant the cancer had spread (170 [67%]). While most (171 [80%]) recognized that an unremarkable chest radiography was good news, only 44 participants (21%) correctly understood that a clinician saying their radiography was impressive was generally bad news. In each of the paired phrases comparing jargon vs nonjargon approaches, the nonjargon phrase was understood significantly better (P < .001).Conclusions and RelevanceThese findings suggest that several common phrases are misunderstood when used in a medical setting, with the interpreted meaning frequently the exact opposite of what is intended.