An anorexia nervosa patient with hypophosphatemia secondary to starvation and laxative abuse is reported. During the course of refeeding by tube with a high caloric balanced formula, the patient's serum phosphorous dropped from low normal on admission (2.7 mg/dl) to 0.4 mg/dl aggravated by an overdose of laxative she had stolen from the medicine cart. This required ICU monitoring during intravenous phosphorous administration. This case points out the potential hazard of oral realimentation in a severely cachectic anorectic.