Sigmoid colon diverticulosis is commonly seen in both the surgical outpatient and emergency departments. Rarely, these sigmoid diverticulum, which usually range from 2–3mm to 2cm in size, can enlarge to more than 10 times. This is due to a ball-valve type mechanism that traps colonic gas inside the sigmoid diverticulum causing it to gradually enlarge. Patients with a giant sigmoid diverticulum (GSD) must be investigated thoroughly as 2 per cent of patients will present with a colonic carcinoma either within or distal to the GSD. Clinical symptoms of a GSD can range from chronic abdominal pain, altered bowel habits, abdominal distention, weight loss, bleeding, perforation, fistula formation, or bowel obstruction. CT and plain abdominal x-ray is the investigation of choice for its diagnosis. Barium enema is useful to determine the presence of a carcinoma within the GSD. Sigmoidoscopy is useful to rule out a distal colonic carcinoma. This is the first published case where nocturnal diarrhoea is the primary differentiating symptom in the patient. The treatment of choice for a GSD is complete resection of the diverticulum and/or the adjacent sigmoid colon. This can be performed with a primary anastomosis or a double-stage procedure.