The growth of Ge on Ge(111) has been studied in situ by X-ray diffraction and reflectivity. For well defined geometries the scattered X-ray intensity is extremely sensitive to atomic-scale surface morphology. For substrate temperatures up to 200 degrees C oscillations in the reflected and diffracted yields are observed, which are indicative for two-dimensional nucleation. Curves showing reflectivity versus perpendicular momentum transfer Q_z yield the height distribution of the islands. The use of X-rays allows for a straightforward 'single-scattering' interpretation of the intensities, as opposed to the use of reflection high-energy electron diffraction where multiple-scattering effects have to be taken into account.