The article reports on two cases of complete duplication of the small intestine in an infant of 7 months of age (female) and a boy aged 3 1/2 years. The almost complete lining of the duplicated small intestine with gastric mucosa resulted in massive haemorrhages. These haemorrhages, in conjunction with ileus, were the indications for an operation. Mucosectomy was performed in the region of the duplication. Such removal of the mucosa is recommended in complete duplication of the small intestine and in partial tubular forms.