Thin film growth of tetracene on Ag(1 1 0) has been investigated by using scanning tunneling microscopy (STM). In the monolayer regime, the tetracene molecules formed islands of ordered structure, which is commensurate (4-fold periodicity) in the [1 1 0] direction, but incommensurate in the [0 0 1] azimuth, with the substrate. All the tetracene molecules align regularly with their longer axes parallel to the [0 0 1] direction, and with their molecular planes parallel to the surface. At multilayer coverages, the tetracene molecules form a crystalline film in a novel 3D orthorhombic structure, with their orientations remained unchanged. Growth of tetracene on Ag(1 1 0) is in the layer-by-layer growth mode. © 2004 Elsevier B.V. All rights reserved.