The majority of follicles contain only a single oocyte. However, it has been shown that more than two oocytes can exist within the same follicle. These follicles have been well documented during fetal development, but their presence in adult ovaries is an intriguing physiologic phenomenon. Apoptotic pathway members, locally produced factors, circulating hormones and steroid factors may be involved in their persistence. The origin and fate of these structures, as well as their contribution to ovulation and fertility in adult females, are discussed in this review