Background Dietitians are trained to identify optimal food choices for clients based on medical state and lifestyle. Orthorexia nervosa (ON) is a proposed disorder related to obsessions about eating healthfully; eating disorders (ED) are serious mental illnesses with symptoms related to eating, body image, and self-esteem. Both ON and EDs are more common amongst dietitians than the general population. Objective This study examined the prevalence of ON and EDs in dietitians in the United States and, amongst this sample, assessed whether the presence of ON symptoms related to symptoms of EDs, including weight, shape, eating, and restraint. Design A cross-sectional design compared responses for participants after dividing into three groups: those scoring at-risk for ON, those with a current or past ED, and a comparison group. Participants A sample of 2,500 registered dietitians were invited to complete surveys electronically; 636 responses were received. Main Outcome Measures Scores on the ORTO-15 and Eating Disorder Examination Questionnaire (EDE-Q) determined prevalence of ON and EDs. Differences in these measures, and body mass index (BMI) were compared in the three groups. Statistical Analyses Analysis of Variance (ANOVA) and Chi-square analyses compared the groups. Results For the entire sample, scores on the ORTO-15 suggested 49.5% were at risk for ON, and scores on the EDE-Q suggested 12.9% were at risk for an ED, with 8.2% of dietitians self-disclosing treatment for an ED. Both the group disclosing ED treatment and the group at risk for ON had a lower mean BMI, lower scores on the ORTO-15 and higher scores on the EDE-Q and all its subscales than the comparison group. Conclusions Clarifying the relationship between ON and EDs is warranted, as ON symptoms appear to be associated not only with disturbances in eating but also with elevated shape and weight concerns.