The crystal growth of trans-azobenzene (diamegnetism) has been investigated in a magnetic field of 80 kOe. The crystallographic axes are determined by X-ray diffraction and compared with the magnetic axes. The crystals grow so that the magnetic chi(3) axis is parallel to the direction of the field. The orientation is explained by the magnetic anisotropy (chi(2) < chi(1) < chi(3)) Of the crystals. Since the magnetic energy has a minimum in the chi(3) direction, the crystals containing a considerable number of unit cells can be stabilized by rotating in this direction against thermal disordering.