Oral phosphosoda is increasingly being used as a bowel preparation for colonoscopy, as it requires that a much smaller volume be ingested and is equally effective and less costly than polyethylene glycol-based electrolyte solutions. Oral phosphosoda has a good safety record, but complications of its use may occur. We describe a patient who died as a result of severe hyperphosphatemia after an oral phosphosoda bowel preparation. A 55-year-old man was admitted with rectal bleeding, abdominal pain, and vomiting. He had a history of diabetes, hypertension, and end-stage renal disease and had successful renal transplant 3 years prior. His initial serum creatinine, calcium, phosphate, and electrolyte levels were normal. He vomited after polyethylene glycol-based electrolyte solution, and an alternate bowel preparation with oral phosphosoda was recommended. He received 90 mL of oral phosphosoda as a single dose. Six hours later, he had cardiorespiratory arrest and was found to have hyperphosphatemia (serum phosphate, 17.8 mg/dL), a high anion gap acidosis, hypoxia, and oliguric renal failure. Resuscitation was unsuccessful. Autopsy showed ischemic colitis. We conclude that bowel preparation with phosphosoda may be associated with severe complications and should be avoided if there is any suggestion of impaired renal function or poor gut motility.