The ultrasonographic appearance of ovaries and uterus during weight-gain in patients with anorexia nervosa is described. In 11 patients who had sequential scans, ovarian volume on admission was considerably smaller than that of normal women but increased logarithmically with weight-gain. When body mass index (BMI) reached 17 kg/m2, ovaries were shown to contain multiple small cysts in all cases. In 5 patients further weight-gain led to the appearance of a dominant cyst; average BMI was approximately 19 kg/m2 at this stage. The changes in ovarian morphology resembled those of normal pubertal development. These results lend support to the suggestion that hypothalamic-gonadal axis dysfunction in anorexia nervosa is a concomitant of starvation; in the management of infertility, an ultrasonographic appearance of cystic ovaries should alert the clinician to the likelihood of undernutrition as the primary disorder in need of treatment.