Objective: Epidemiological studies suggest that the incidence of anorexia nervosa (AN) is increasing in younger populations, with some evidence that clinical differences occur between early onset (EO) and later onset (LO) AN, which may impact prognostic outcomes. The current study sought to compare eating disorder (ED) symptomatology, psychological distress and psychosocial function between EO- and LO-AN in a large sample of treatment-seeking patients with a diagnosis of AN.Methods: Participants included 249 individuals with a diagnosis of AN who were assessed at an outpatient ED service. The sample was divided into two groups based on age of onset (AOO) using a median split (median AOO=16); those with an AOO ≤16 years (N=128) were termed ‘EO-AN’ and those with an AOO of > 16 years (N=121) were termed ‘LO-AN’. Comparisons were made between AOO groups on assessments of ED symptomatology, psychological distress and psychosocial function. Results: EO-AN patients reporteda significantly longer illness duration (p<.001), significantly higher ED symptomatology (p=0.005), dysmorphic concern (p=0.02), stress (p=0.011), anxiety (p=0.023), and cognitive inflexibility (p=0.042), compared to the LO-AN group.Discussion: These findings suggest that clinical differences do occur according to AOO in AN wherebyEO-AN may represent a more severe form of illness. Treatment strategies which specifically address patients with EO-AN may improve long term health outcomes and recovery.