Populations of Callirhytis cornigera (Osten Sacken) and its associated community of natural enemies and inquilines were monitored on pin oak, Quercus palustris Muenchhausen, in Lexington, KY, from 1997 to 1999. The gall wasp has alternating agamic and sexual generations that differ morphologically and develop in multichambered galls on branches and single-chambered galls on leaves, respectively. There was a strong association between maximum gall diameter and the number of total stem gall inhabitants, such that proportionately more C. cornigera survived and fewer were parasitized as stem gall diameter increased. The most abundant natural enemies of the agamic generation included the hymenopteran parasitoids Sycophila spp. (Eurytomidae) and Ormyrus labotus Walker (Ormyridae), and the clerid predator Phyllobaenus verticalis (Say). The most abundant inquilines in stem galls were the cynipids Synergus sp. near lignicola and Ceroptres sp., and the dogwood borer, Synanthedon scitula (Harris) (Lepidoptera: Sesiidae). In leaf galls, Aprostocetus sp. was the most abundant parasitoid, and Ceroptres sp. was the only inquiline. The unique aspects of the C. cornigera gall system are discussed, including the relative abundance, emergence phenology, and host relationships of C. cornigera and its associated natural enemies and inquilines.