Protein-losing enteropathy occurs in patients following the modified Fontan procedure. Treatment is still controversial. We describe a boy who developed protein-losing enteropathy 18-months after an extracardiac Fontan procedure. Treatment with calcium for hypocalcemia attenuated the protein loss with subsequent normalization of serum total protein and albumin levels. Decrease of oral calcium and subsequent decrease of serum ionized calcium level were associated with relapse of hypoalbuminemia. This was again treated successfully with calcium and vitamin D replacement.