Magnesium (Mg) is the fourth most abundant cation in the body and plays a key role in numerous cellular functions such as glycolysis and energy metabolism. Its deficit may cause gastrointestinal disturbances, cardiovascular and neurological diseases. Among the latter, the symptoms may range from muscle weakness and numbness, to lethargy, hyperreflexia, ataxia, tetany, convulsions and coma. We report the case of a man of 65 with short bowel syndrome secondary to extensive bowel resection for sigma neoplasm and subsequent peritonitis, with end ileostomy, who presented several episodes of tonic-clonic seizures secondary to severe magnesium deficiency as a result a decrease in intestinal absorption of losses for high debit ileostomy. After beginning treatment with intravenous magnesium (iv) resulted in plasma levels normalize. Subsequently instituted dietary and pharmacologic treatment recommendations as well as magnesium and high-dose oral calcitriol to increase their absorption.