Micronization of ibuprofen by a rapid expansion of supercritical solutions (RESS) process has been explored for a wide range of operating conditions, including temperatures above the melting point of ibuprofen. Morphologies, particle sizes (PSs), and particle size distributions (PSDs) have been analyzed by scanning electron microscopy and the crystallinity has been evaluated by X-ray diffraction measurements. Possible structural changes in the drug after supercritical fluid processing were evaluated by Fourier transform infrared spectroscopy. The effects of different pressures (100-350 bar), temperatures (308-353 K), and nozzle diameters (100-200 mu m) on the drug precipitation have also been investigated. The morphology of the precipitated particles was improved in the majority of cases in comparison to the raw material, and the PS decreased. In general, higher pressures led to smaller particle sizes. The smallest particle sizes were obtained at 318 and 333 K, and precipitated powder was obtained even at temperatures above the melting point of ibuprofen. A larger nozzle diameter led to a larger particle size.