The hair follicle is considered to be a model system for studying organogenesis. In our initial study using mouse cells (Zheng et al., 2005) we found that new hair follicle formation always starts from an epithelial platform: the epidermal cells aggregate, the aggregates encyst, and from the periphery of the cysts, centrifugally, hair buds, pegs, and follicles form. In this report, we extend our initial study to four distantly related mammals: opossum, rat, dog and human. We find that in these four species, plus mouse, the most trichogenic cells are found in the earliest stages of hair follicle development and that the cellular mechanism of new hair follicle formation starting from dissociated cells is largely the same. These studies suggest that there is essentially one way by which dissociated mammalian skin cells form a new hair follicle in vivo and that this mechanism has been highly conserved.