Mg deficiency is a frequent complication of inflammatory bowel disease (IBD) demonstrated in 13-88% of patients. Decreased oral intake, malabsorption and increased intestinal losses are the major causes of Mg deficiency. The complications of Mg deficiency include: cramps, bone pain, delirium, acute crises of tetany, fatigue, depression, cardiac abnormalities, urolithiasis, impaired healing and colonic motility disorders. Serum Mg is an insensitive index of Mg status in IBD. Twenty-four-hour urinary excretion of Mg is a sensitive index and should be monitored periodically. Parenteral Mg requirements in patients with IBD are at least 120 mg/day or more depending upon fecal or stomal losses. Oral requirements may be as great as 700 mg/day depending on the severity of malabsorption.