People use others' dress to make assumptions, including how they believe the wearer will behave. Observers then adjust their behavior in response to the anticipated behavior of the wearer. Physician or nurse dress affects the degree to which patients perceive the medical professional as confident, experienced, competent, mature, trustworthy, and professional. Dietitian dress has not been studied. Our purpose was to identify 1) the current level of formality of dress of registered dietitians (RD), 2) characteristics of dress codes, 3) the effect of RD dress on patient/client perceptions of professional traits, and 4) the level of formality at which an RD is perceived as being most professional. Phase I Respondents were randomly selected from the American Hospital Association database and the national WIC directory. A total of 972 managers (449 WIC and 523 hospital nutrition services) completed a survey about their facility's dress code policy for RDs, and how the facility's dietitians dress for work. Data showed that at most WIC clinics dietitians dress in Semi-Casual (khaki pants/collared knit top) attire while most hospitals dietitians dress in Business Casual II (dress slacks/knit shirt) attire. Over half of all managers surveyed felt that dietitian dress was important and a priority. Phase II Respondents were patients/clients of a hospital or WIC clinic in Illinois, Virginia, or Utah. Respondents gave demographic information and rated pictures of a dietitian in nine sets of clothing on eight characteristics: empathetic, competent, approachable, credible, organized, effective, professional, and confident. Respondents identified the dietitian with whom they would most and least prefer to have nutritional counseling. A total of 582 surveys were collected. These data showed that WIC participants and hospital patients most preferred the dietitian to dress in Business Casual (dress slacks/collared dress shirt) with a lab coat; this attire also received the most positive/desirable Professional Characteristic Scores. All respondents least preferred the dietitian dressed in Casual (jeans/knit shirt) attire; this attire received the least positive/desirable Professional Characteristic Scores. Only 1.1% of WIC and 8.1% of hospital dietitians regularly wear dress slacks, a collared shirt, and a lab coat, the patients'/clients' most preferred dress for dietitians.