Premenarchal anorexia nervosa (AN) represents a specific subtype of AN, defined by an onset before the menarche in females, involving unique endocrine and prognostic features. The scarce data on this condition lack case–control and follow-up studies. This is a case–control, observational, naturalistic study, involving participants with premenarchal AN (premenarchal girls presenting to the study center newly diagnosed with AN) treated with a multidisciplinary hospital intervention, compared to postmenarchal AN individuals on clinical, endocrine, psychopathological, and treatment variables. The rate of rehospitalizations on a 1-year follow-up after discharge and respective prognostic factors were assessed with a Kaplan–Meier analysis and Cox regression model. The sample included 234 AN participants (43, 18.4% with premenarchal and 191, 81.6% with postmenarchal AN). When compared to postmenarchal, premenarchal AN individuals presented with lower depressive scores (Self-Administered Psychiatric Scales for Children and Adolescents (SAFA)) (U= 1387.0,p= 0.010) and lower luteinizing hormone (LH) levels (U= 3056.0,p= 0.009) and were less frequently treated with antidepressants (X2= 5.927,p= 0.015). A significant predictive model of the risk of rehospitalization (X2= 19.192,p= 0.004) identified a higher age at admission (B= 0.522,p= 0.020) and a day-hospital (vs inpatient) treatment (B= 3957,p= 0.007) as predictive factors for rehospitalization at 1-year, independent from the menarchal status.Conclusion: This study reports the clinical and treatment characteristics of premenarchal AN in one of the largest samples available in the current literature. Specific clinical features and prognostic factors for rehospitalization at 1-year follow-up were identified. Future studies should longitudinally investigate treatment-dependent modifications in endocrine and psychopathological measures in this population.What is Known:• Premenarchal Anorexia Nervosa (AN) is a subtype of AN characterized by its onset before menarche in females and is associated with unique endocrine and prognostic features.What is New:• Individuals with premenarchal AN may display specific clinical profiles, with lower depressive symptoms and luteinizing hormone levels than postmenarchal controls.