Radiopaque microspheres of sizes ranging from 0.2 to 1.4 mu m were formed by the dispersion polymerization of the monomer 2-methaeryloyloxyethyl(2,3,5-triiodobenzoate) in 2-methoxyethanol. The effects of various polymerization parameters, including the monomer concentration, initiator type and concentration, and stabilizer molecular weight and concentration, on the molecular weight, size, and size distribution of the particles were elucidated. The characterization of these iodinated microspheres was accomplished with routine methods such as Fourier transform infrared, nuclear magnetic resonance, thermogravimetric analysis, differential scanning calorimetry, gel permeation chromatography, scanning electron microscopy, Brunauer-Emmett-Teller measurements, and elemental analysis. Because of the presence of iodine atoms in these microspheres, they were expected to possess a radiopaque nature. The radiopacity of these particles dispersed in water and in the dry state was demonstrated with an imaging technique based on X-ray absorption usually used in hospitals. These novel radiopaque microspheres may be used for different X-ray imaging needs, such as blood pooling, body organs, embolization, dental compositions, implants, prostheses, and nanocomposites. (c) 2006 Wiley Periodicals, Inc.