Objective: This pilot study investigated predictors, moderators, and mediators of outcome and readmission in adolescents receiving specialist inpatient treatment for anorexia nervosa. Method: Adolescents (n = 40) aged between 14 and 17 years (mean = 15.42) were assessed at admission and discharge from a specialist inpatient programme and again at three-month follow-up on the following outcome variables: eating disorder pathology, quality of life (QOL), and body mass index (BMI) centile. Readmissions to hospital were recorded over the three months post-discharge period. Potential predictors were drawn from theoretical models. Results: Readmission during the three-month follow-up period was less likely for first presentations. Higher baseline purging, concern over mistakes, perfectionism, ineffectiveness, and mood intolerance were associated with higher levels of eating disorder pathology and poorer QOL over all points of follow-up. Driven exercise moderated weight outcomes such that higher levels of baseline exercise resulted in a lower BMI centile at follow-up. Greater weight gain during treatment predicted higher BMI centile at follow-up, and increased perfectionism during treatment predicted a greater likelihood of being readmitted within three months of discharge. Conclusions: Weight gain during inpatient treatment should be encouraged to improve later weight outcomes. Focusing on the prevention of growth in perfectionism may be useful in improving psychological outcomes as will prioritising the elimination of purging and improved emotional regulation and self-efficacy. Efforts should be made to reduce driven exercise to promote better weight-related outcomes.