A 49-year-old man was seen with an unusual complication of diverticulitis--a giant sigmoid diverticulum. This patient had undergone an extensive workup during a 5-year period, ranging from multiple extensive gastroenterology evaluations and procedures to an eventual psychiatric evaluation to rule out the possibility of a functional cause for his chronic, intermittent abdominal pain. Later, an accurate diagnosis of a giant sigmoid diverticulum resulted in an en bloc resection of the sigmoid colon and cyst. The patient had an uncomplicated recovery with no return of his previous symptoms. The authors review the many proposed causes of the giant sigmoid diverticulum and possible differential diagnoses. Initially, the diagnosis is usually missed as plain roentgenograms, upper and lower gastrointestinal x-ray studies, and computed tomography scans generally show no abnormality. Management methods are also discussed.