The gametophytic generation of Cheilanthes pilosa (Pteridaceae), including spore germination, morphological development of the gametophytes, major vegetative features and sexual expression, was studied. In C. pilosa spore germination was of the Vittaria model and the developmental pattern was intermediate between Adiantum and Ceratopteris models. Adult gametophytes were cordate and hairy, with unicellular hairs located in the margins and both the ventral and dorsal surfaces of the prothalli. Gametangia were of the normal type described for leptosporangiate ferns. In C. pilosa populations the gametophytes produced at first instance a high proportion of female gametophytes, few male gametophytes developed and most of the female gametophytes became bisexual with time. Thus, although outbreeding is possible, this species seemed to be promoting intragametophytic selfing as the major reproductive strategy.