Colonic duplication is a rare congenital abnormality that can present diagnostic difficulties to the radiologist. Three new cases are reported to illustrate the different types of this anomaly. A classification is presented in which the condition is divided into two types: in type I lesions the duplication is limited to the colon and in type II lesions there are associated duplications of the genito-urinary tract. The wide spectrum of possible pathological, clinical and radiological features are reviewed.