A case of obstruction of the colon by a solitary, large gall-stone is described. This rare event usually occurs in elderly females in whom there is frequently an underlying pathological condition at the site of obstruction in the colon. The calculus usually migrates via a cholecystocolic fistula. Diagnosis may be assisted by plain abdominal X-ray and contrast radiography. Immediate operative treatment should be tailored to the patient's general condition and the nature of the pathological changes.