Neutron diffraction measurements on a single crystal of dysprosium show that the magnetic structurein the antiferromagnetic region between 179° and 87°K closely resembles a helical-type arrangement of theatomic moments. In this arrangement the moments within a hexagonal layer are aligned parallel and pointin a direction perpendicular to thecaxis of the crystal. The moment direction in adjacent layers is rotatedby a specific angle which is dependent on the temperature of the sample. A slight modification of thisstructure exists below about 140°K, and a transition to ferromagnetism occurs at 87°K.