The organic material 3,4,9,10-perylene-tetracarboxylicacid-dianhydride (PTCDA) evaporated onto Ag(1 1 1) substrates can be prepared as highly ordered thin films. By employing a variety of characterization methods, we find that the structural, morphological, and growth character as well as the optical properties strongly depend on preparation parameters. By increasing the substrate temperature between 180 and 420 K we observe a transition from a homogeneous layer-by-layer film growth with a smooth and small-grained morphology towards the formation of large, isolated crystallites on a complete coverage of two strained layers, i.e., Stranski-Krastanov growth. The present results contribute to a fundamental understanding of organic epitaxial growth. (C) 2003 Elsevier Science B.V. All rights reserved.