The synthesis of cadmium oxide from a gel of cadmium hydroxide has been followed in situ using unique combinations of X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy, and small-angle X-ray scattering (SAXS). XRD and XAFS enable the crystallography, particle size, and local structure to be quantified as the hydroxyl gel converts into cadmium oxide around 182 degrees C, SAXS measures the evolving microstructure, with cadmium oxide growing dendritically in a fractal geometry, initially from rough nanoparticles. Major growth and densification takes place between 325 and 550 degrees C. The implications for characterizing the precipitation of cadmium oxide nanoparticles in zeolitic hosts are considered.