There is scant research on the clinical utility of differentiating International Classification of Diseases (ICD) 10 diagnoses F50.0 anorexia nervosa (typical AN) and F50.1 atypical anorexia. We reviewed systematically records of 47 adolescents who fulfilled criteria for ICD‐10 F50.0 (n = 34) or F50.1 (n = 13), assessing the impact of diagnostic subtype, comorbidity, background factors and treatment choices on recovery. Atypical AN patients were significantly older (p = 0.03), heavier (minimum body mass index 16.7 vs 15.1 kg/m2, p = 0.003) and less prone to comorbidities (38% vs 71%, p = 0.04) and had shorter, less intensive and less costly treatments than typical AN patients. The diagnosis of typical versus atypical AN was the sole significant predictor of treatment success: recovery from atypical AN was 4.3 times (95% confidence interval [1.1, 17.5]) as likely as recovery from typical AN. Overall, our findings indicate that a broader definition of AN may dilute the prognostic value of the diagnosis, and therefore, ICD‐11 should retain its distinction between typical and atypical AN. Copyright © 2015 John Wiley & Sons, Ltd and Eating Disorders Association.