The wood and leaf anatomy of the 6 genera of the Cecropiaceæ are described in detail. The anatomical data are compared with those of the allied Moraceæ and Urticaceæ. The relationship between habit, habitat, and anatomical characters is discussed, as well as the relationships within the family. Based on anatomical data the genus Poikilospermum should be included in the family Urticaceæ.