Thin amorphous indium-tin-oxide (ITO) films were deposited on unheated Si(100) wafers by dc magnetron sputtering from a metallic target (In:Sn = 90:10) with oxygen as reactive gas. In-situ grazing incidence x-ray diffractometry (GIXRD) measuring of ITO(222)-reflection intensities was performed during annealing in a vacuum chamber (10(-5) mbar) at temperatures that ranged between 220 and 240 degreesC. The crystallization process was studied depending on annealing time and temperature. Additionally the films were investigated by XPS, AFM and grazing incidence x-ray reflectometry (GIXR) before and after annealing. Kinetic growth parameters were determined from the intensity data. A discussion of the data is presented using the JOHNSON-MEHL-AVRAMI-equation. The reaction order n, which describes the crystallization mechanism, was found to be between 2.4 and 3, indicating a two-dimensional growth. From the temperature dependence of the rate constant the activation energy for the amorphous-to-crystalline transformation was found to be E-A = 74 kJ/mol.