The determination of the treatment goal weight for adolescents with a restrictive eating disorder (ED) and a prior history of obesity, such as in atypical anorexia nervosa (AAN), represents an ongoing challenge for clinicians. This determination is particularly complex given competing interests of physical recovery from significant weight loss, mental recovery from ED psychopathology, and the medical comorbidities associated with obesity. We report the case of a 15-year old female with a history of obesity and irregular periods who presented with significant weight loss and absence of menses for 3 months. She was hospitalized for severe malnutrition and bradycardia, initiated family based treatment, and regained periods. However, her vital sign instability and eating disorder cognitions did not resolve until she reached a weight at which point her periods again ceased due to polycystic ovary syndrome. This case highlights the need for regular monitoring during weight recovery and the clinical challenge of determining the treatment goal weight in adolescents with EDs and prior obesity.