CeCuSn, which forms in the hexagonal CaIn2-type of structure, orders antiferromagnetically at 8.6 K. A second maximum at about 7.35 K seen in the temperature dependence of the specific heat indicates a rearrangement of the antiferromagnetic structure. The antiferromagnetic ordering is also reflected in the temperature dependence of the electrical resistivity. Upon application of magnetic fields up to 5 T, a complex development of magnetic phases can be followed by monitoring the temperature dependencies of the magnetization and the specific heat. In the B-T diagram, three different magnetic phases were detected and their boundaries could be determined.