BACKGROUND Anorexia nervosa, a condition characterized by marked caloric restriction and low insulin like growth factor-1 levels, would be expected to cause short stature. However, this disorder is also associated with hypogonadotropic hypogonadism and high growth hormone levels. Delays in growth-plate closure from associated hypogonadism may result in a longer period of time available for statural growth with protective effects on stature. In addition, growth hormone may have direct effects on the growth plate independent of insulin-like growth factor 1 to increase statural growth. OBJECTIVE To determine the impact of undernutrition, hypogonadism, and acquired growth hormone resistance on height in adolescents with anorexia nervosa (aged 12-18 years), we examined 208 girls: 110 with anorexia nervosa and 98 controls of comparable chronological age. Sixty-three girls with anorexia nervosa and 79 controls were followed prospectively over 1 year. Mean duration of illness was 11.6 +/- 13.2 months. In a subset, overnight growth hormone sampling was performed every 30 minutes for 12 hours, and fasting insulin-like growth factor 1 levels were obtained. RESULTS The difference between height and target height and between predicted adult height and target height did not differ between the groups, indicating preservation of height potential. The groups had comparable bone age, but bone age was lower than chronological age in girls with anorexia nervosa. Girls with anorexia nervosa had lower insulin-like growth factor 1 levels and higher nadir growth hormone levels than those of controls. Nadir growth hormone levels predicted height SD scores and predicted adult-height SD scores in controls but not in the girls with anorexia nervosa. In girls with anorexia nervosa, insulin-like growth factor 1 and duration of illness predicted height measures. Height SD scores of <0 were more likely after 32 months of illness and at insulin-like growth factor 1 levels of <134 ng/mL. Delayed baseline bone age predicted subsequent increases in height SD scores in immature girls with anorexia nervosa. CONCLUSIONS Our data suggest that preservation of height potential in this cohort of girls with anorexia nervosa may be a consequence of delayed bone age. Hypogonadism may negate the deleterious effects of undernutrition on stature by allowing for a longer duration of growth.