The McKittrick-Wheelock syndrome, a rare disorder, is caused by fluid and electrolyte hypersecretion from a rectal tumour and patients can develop a depletion syndrome characterised by severe dehydration, hyponatraemia, hypokalaemia and metabolic acidosis. We present a case of a 62-year-old man who presented with chronic diarrhoea that had resulted in numerous previous hospital admissions. On physical exam, the patient showed signs of volume depletion. A soft polypoid mass was appreciated on digital rectal examination. Laboratory tests showed renal failure and significant electrolyte abnormalities. Colonoscopy revealed a large, friable mass in the rectosigmoid region. Biopsies were consistent with tubolovillous adenoma. Subsequently, the patient underwent surgical resection, which on pathology exhibited evidence of high-grade dysplasia, and the patient was diagnosed with McKittrick-Wheelock syndrome. It is essential to identify this condition in a timely manner as it is associated with high morbidity and complications, some of which may be life threatening.