A congenital diverticulum of the small intestine is a condition with only a low morbidity and is generally a Meckel's diverticulum. There is, however, another congenital malformation, which can closely resemble a Meckel's diverticulum, but has another etiology, the tubular duplication of the small intestine. The authors point out the embryologic, anatomic and histological findings between these different but very similar malformations. It seems that the diagnosis of duplication is not often considered when finding a diverticulum of the small intestine and such a malformation is too easily called a Meckel's diverticulum.