Ift88 is a component of the intraflagellar transport complex required for formation and maintenance of cilia. Disruption of Ift88 results in depletion of cilia. The goal of the current study was to determine the role of primary cilia in ovarian function. Deletion of Ift88 in ovary using Cre-Lox recombination in mice resulted in a severe delay in mammary gland development including lack of terminal end bud structures, alterations in the estrous cycle, and impaired ovulation. Because estrogen drives the formation of end buds and Cre was expressed in the granulosa cells of the ovary, we tested the hypothesis that addition of estradiol to the mutant mice would compensate for defects in ovarian function and rescue the mammary gland phenotype. Mammary gland development including the formation of end bud structures resumed in mutant mice that were injected with estradiol. Together the results suggest that cilia are required for ovarian function. © 2008 Wiley-Liss, Inc.