To clarify the clinical significance of elevation of serum aminotransferase levels in anorexia nervosa, we analyzed the relationships of serum aminotransferase levels to other serum biochemistry and physical conditions before and during refeeding therapy in 101 patients with anorexia nervosa. Before refeeding therapy, body mass index (BMI) was distributed from 9.9 to 16.4 kg/m2 (13.2 +/- 1.3, mean +/- SD), and 29 patients (28.7%) showed abnormally high aminotransferase levels. Among 17 patients with a BMI of less than 12 kg/m2, the aminotransferase level was abnormally high in 13 patients (76%). Incidence and severity of serum aminotransferase elevation were greater in the patients with lower BMI. The groups with high serum aminotransferase levels had a lower body temperature, lower pulse rate, and higher incidence of other biochemical abnormalities than the group with normal serum aminotransferase levels. These findings indicate that aminotransferase elevation develops at a high incidence in anorectic patients with a critically life-threatening condition, and it is a sign of multiorgan failure requiring urgent calorie repletion. This type of aminotransferase elevation is to be distinguished from refeeding-induced aminotransferase elevation.