The structure of cubanite, CuFe2S3, was known from an earlier trial-and-error investigation. In this structure both iron and copper atoms are tetrahedrally coordinated to sulfur. The structure is peculiar in that the Fe tetrahedra share an edge giving rise to a short Fe-Fe distance which probably corresponds to a bond. Because of the ferromagnetism of cubanite it is important to know the details of the structure with accuracy. To this end the refining of the structure is herewith reported. The refining process was carried out in three stages 1 by electron density projections, 2 by plane sections through the three-dimensional distribution of electron density, and 3 by differential line syntheses through each atom. In the refined structure, the Fe atoms are found to be coordinated to four S atoms at distances of 2.29, 2.28, 2.27, 2.25 A, and one Fe atom at 2.81 A. The shared tetrahedral edge is somewhat shortened, having a length of 3.61 A, as compared with the other edges of 3.71, 3.72, 3.73, 3.84, and 3.84 A.