Objective Predictive values of acute phase metabolic abnormalities of anorexia nervosa (AN) have seldom been studied. As early postrestoration weight loss is associated with poor outcome, discharge biologic parameters were assessed to detect an association with 2‐month follow‐up weight loss as a proxy to poor outcome. Method Fasting plasma levels of leptin, acyl‐ghrelin, obestatin, PYY, oxytocin and BDNF were measured in 26 inpatients, at inclusion, at discharge and 2 months later. A body mass index less than 18 2‐month postdischarge was considered a poor outcome. Results Nineteen patients (73%) had a fair outcome and seven (27%) had a poor one with a mean loss of 0.69 versus 4.54 kg, respectively. Only discharge leptin levels were significantly higher in fair versus poor outcome patients (14.1 vs. 7.0 ng/ml, p = 0.006). The logistic regression model using discharge leptin, acyl‐ghrelin, obestatin, oxytocin, PYY and BDNF levels as predictors of outcome disclosed a nearly significant effect of leptin (p < 0.10). Receiver operating characteristic analysis showed 11.9 ng/ml was the best value of threshold. Neither clinical variables differed according to outcome. Conclusion Leptin level may be a biomarker of early weight relapse after acute inpatient treatment of AN. Its clinical usefulness in monitoring care in AN should further be determined. Highlights Basal leptin level may be a marker to determine end‐of‐weight restoration. Basal leptin level may have a better predictivity than body mass index for prognosis after weight‐restoration. This marker could potentially help a better allocation of preventive scarce resources and a better development of appropriate methods of relapse prevention.