Introduction Inpatient treatment for eating disorders is a scarce, expensive resource. We aimed to examine length of stay (LOS) in specialist Scottish inpatient units and to identify relationships between LOS, outcome measures and other factors. Method Audit of 206 admissions (89 adolescents and 117 adults) between 2009 and 2011 to all seven inpatient units in Scotland that specialize in the treatment of eating disorders. Data was collected retrospectively from electronic database and patient case files. Results Physical and psychological eating disorder symptoms improved significantly during specialist inpatient admissions. Mean LOS for adolescents was 141.4 days and for adults 113.0 days. Patients gained weight during admission and increased LOS correlated with increased weight gain. Treatment under the Mental Health Act or with nasogastric feeding increased LOS in adolescents. Conclusion Future efforts should be invested in prospective studies, including several years' post‐discharge follow‐up, to explore correlations with LOS and guide treatment decisions. Copyright © 2013 John Wiley & Sons, Ltd. Key Practitioner Message Inpatient treatment in specialist eating disorder units is associated with nutritional and psychological benefits in adults and adolescents. Treatment requiring legal detention or nasogastric feeding involves longer admission. Further research is needed to see whether benefits are lasting.