Anorexia nervosa (AN) is life-threatening because of many physical complications, hence a quantitative indicator for early therapeutic intervention through hospitalization is needed. Here, we compared the demographics of 21 patients with AN who required intensive treatment in the internal medicine ward and those of 61 patients with AN who directly admitted to the psychiatric ward. We developed a risk score for severe physical complications in patients with AN, by using six items with significant differences between two groups; body mass index, blood urea nitrogen, corrected calcium, albumin, aspartate transaminase, and C-reactive protein (area under the curve = 0.824).