The molecular sizes of four star microgels, synthesized by atom transfer radical polymerization of poly(methyl methacrylate) (PMMA) with ethylene glycol dimethacrylate as the cross-linker, have been investigated by light scattering methods and transmission electron microscopy (TEM). Gel permeation chromatography right-angle laser light scattering performed with a triple detector system and dynamic light scattering together confirm that individual particles of one star microgel in tetrahydrofuran and styrene solutions possess mean diameters of 31 and 18 nm, respectively. Complementary TEM reveals that another star microgel appears as discrete particles measuring 18-30 nm in diameter when added to styrene monomer subsequently polymerized to form a solid matrix. These particles likewise undergo macrophase separation to form microgel-rich domains consisting of nanoscale PMMA channels. Additional TEM examination of a star microgel deposited by dilute solution casting provides direct evidence for the existence of individual microgel molecules with a mean (dry) diameter of similar to15 nm.