Hypertonic sodium phosphate enemas are available for relief of constipation. They are widely used as colorectal laxatives because of their efficacy and because most patients tolerate the preparation well. Nevertheless, their use has been associated with decreases in intravascular volume as well as measurable changes in serum phosphorus and calcium levels. Usually these effects are transient and cause no ill effects. Severe toxicity may occur when the osmotically active hypertonic phosphate enema is retained or when it is administered to a patient with a decreased glomerular filtration rate. We report an elderly patient with previously normal renal function who developed severe hyperphosphatemia, hypocalcemia, and cardiac arrest after the administration of hypertonic sodium phosphate enemas for the treatment of an ileus. We review the patient characteristics that increase the risk of adverse effects from hypertonic sodium phosphate enemas and emphasize the danger that moderate dehydration poses when considering the use of these cathartics.