Pelvic ultrasonographic measurements and reproductive hormone levels in 36 patients with anorexia nervosa were followed as they gained weight during inpatient treatment. In 24 patients who were severely malnourished (69% of premorbid weight) the ovaries were small and amorphous and the levels of LH, FSH and oestradiol were very low. Weight gain led to the appearance of multifollicular ovaries when levels of LH and oestradiol remained low but FSH levels had increased resulting in an LH:FSH ratio of less than 1. The emergence of a dominant follicle in 19 patients after weight gain (to 97% of premorbid weight) was accompanied by an increase in uterine area and associated with increased levels of LH and oestradiol and an LH:FSH ratio greater than 2. Among these patients with a dominant follicle at peak weight, 11 menstruated within a month of discharge. The weight at which normal ovarian morphology returned was related to premorbid weight (P less than 0.002) whereas body mass index (BMI) was poorly related. Our findings suggest that pelvic ultrasonography is probably the best indicator of the weight required for full endocrine recovery and offers advantages over sequential hormonal measurements, and is valuable in the management of patients with anorexia nervosa.