Target weights are an arbitrary means of determining return to physical health in patients with anorexia nervosa (AN) and lack reliability and validity. Transabdominal pelvic ultrasound scanning (U/S) offers a more objective method of ascertaining physical well being by the ability to determine reproductive maturity. This study aimed to explore the correlations between the maturity grading on pelvic U/S and weight for height (WfH) ratios and body mass index (BMI) percentiles. Ultrasound studies were performed in 72 female adolescents (aged 11-17 years at intake) with AN. Scans were graded for maturity using published parameters of pelvic maturity and compared with the patient's WfH ratio and BMI percentile. In our sample was a wide variation of WfH ratios and BMI percentiles at each grade of maturity. This supports the view that arbitrary targets for weight, WfH ratio or BMI percentile are likely to be unnecessarily high for some patients and too low for others. We recommend that targets be based upon baseline pelvic U/S grading and follow-up scanning.