The morphology of the ovarian mesothelium (surface epithelium) and of other pelvic and extrapelvic mesothelia was investigated in the rabbit by use of scanning electron microscopy. Villous processes of varied architectural complexity and surface epithelial crypts were found in the ovary but not in the mesothelial linings of the oviduct, uterus, liver, or pelvic and abdominal walls. Both ovarian and extraovarian mesothelial cells possessed abundant microvilli. Fully developed individual cilia and ciliary tufts were seen exclusively in ovarian mesothelia, while abortive or blunted cilia were rarely seen in pelvic but not in extrapelvic mesothelia. A distinct transition in surface configuration was present in contiguous mesothelia. In fact, ovarian mesothelia containing numerous villous processes, crypts, and cuboidal to low columnar cells merged with oviduct and fat mesothelia displaying only flat or low cuboidal cells. Villous processes were often lined by a stratified or pseudostratified epithelium and this histology resembled that of ovarian surface papillomas. Processes were more numerous in smaller ovaries than in larger ovaries where interstitial tissue and corpora lutea were prominent. This study underscores the unique architecture and morphogenetic behavior of the ovarian mesothelium. It also suggests that local factors and/or reproductive patterns may have a role in regulating the growth and development of this important ovarian component.