Purpose: This study aimed to determine the changes in diagnosis that occur in making the transition from Diagnostic and Statistical Manual of Mental Disorders , Fourth Edition (DSM-IV) to Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria in an adolescent medicine eating disorder program. Methods: During the months of September 2011 through December 2012, a data sheet was completed at the end of each new outpatient eating disorder evaluation listing the patient’s gender, age, ethnicity, weight, height, DSM-IV diagnosis, and proposed DSM-5 diagnosis. Distributions were calculated using the Mann-Whitney and Wilcoxon rank sum analyses to determine differences between diagnostic groups. Results: There were 309 patients evaluated during the 16-month period. DSM-IV diagnoses were as follows: anorexia nervosa, 81 patients (26.2%); bulimia nervosa, 29 patients (9.4%); binge eating disorder, 1 patient (0.3%); and eating disorder not otherwise specified (EDNOS), 198 patients (64.6%). By contrast, DSM-5 diagnoses were as follows: anorexia nervosa, 100 patients; atypical anorexia nervosa, 93 patients; avoidant/restrictive food intake disorder, 60 patients; bulimia nervosa, 29 patients; purging disorder, 18 patients; unspecified feeding or eating disorder, 4 patients; subthreshold bulimia nervosa, 2 patients; subthreshold binge eating disorder, 2 patients; and binge eating disorder, 1 patient. Conclusion: Almost two thirds (64.6%) of the 309 patients had a diagnosis of EDNOS based on the DSM-IV criteria. By contrast, only four patients had a diagnosis of unspecified feeding or eating disorder based on the DSM-5 criteria. These data demonstrate that the goal of providing more specific diagnoses for patients with eating disorders has been accomplished very successfully by the new DSM-5 criteria.