This is a report on sexithiophene thin films (6-300 angstrom) grown on TiO2(1 1 0) single crystal surfaces. The films are investigated by atomic force microscopy and both laboratory and synchrotron X-ray diffraction techniques. Different growth stages are identified: after the formation of a first lying monolayer, small clusters are formed. Thicker films show needle like morphologies with two distinct needle directions. The morphology can be assigned to the obtained crystal alignments and a growth model is derived: the oxygen rows of the surface direct the alignment of initially adsorbed molecules parallel to the surface corrugation. Further molecules form small clusters on top of this monolayer. At a sufficient cluster size they merge and crystallize in the so-called low temperature phase with the contact plane {0 1 0} having a mosaicity of 1-2 degrees. Furthermore, the observed crystallites show a distinct in-plane alignment, with a distribution of few degrees which perfectly explains the two needle directions. However, the molecules of the crystallites are slightly rotated to the oxygen rows, which is ascribed to a lattice match effect. Therefore it is concluded that the molecules of the monolayer are integrated in the crystal structure and undergo a slight realignment during 3D crystal growth. Finally the importance of an atomically ordered substrate surface is illustrated by a comparison to a film grown on an intentionally disordered surface leading to standing molecules without in-plane order. (C) 2007 Elsevier B.V. All rights reserved.