The treatment of atypical anorexia nervosa (AN) poses new research and practice challenges for the field of eating disorders. The objective of this study was to describe frontline practitioners' perceptions of differences between adolescents living with atypical versus typical AN, as well as the intervention challenges they experience when working with these adolescents and their families. We followed the principles of fundamental qualitative description and recruited a purposeful sample of practitioners treating adolescent eating disorders to complete a one-on-one semi-structured interview. Conventional content analysis and the constant comparison technique were used for data analysis. A total of 23 practitioners from four countries participated in this study. Practitioners described that adolescents with atypical AN present with higher pre-morbid weights and rates of weight-based teasing compared to their AN peers. Clinical challenges perceived by practitioners to be specific to working with adolescents with atypical AN included: addressing conflicting messages about eating disorders and weight loss, empathizing with a justified fear of weight gain, and increased risk for parental and therapist collusion with the eating disorder. Findings have implications for delivering interventions to adolescents seeking care for atypical AN.