Spermatogenesis in the banana bat (Pipistrellus nanus) from southern Malawi began in the hot, wet season (February to April) and spermatozoa were released to the cauda epididymides at the beginning of the cool, dry season (May). Mating occurred between mid-June and early July, in the middle of the cool, dry season. After mating, spermatozoa were stored by the female until ovulation in August and by the male until at least September. The period of female sperm storage effectively lengthened the reproductive cycle so that early spermatogenesis occurred during the second half of one hot, wet season and births at the beginning of the following hot, wet season. During the period of sperm storage, males and females roosted together and group membership was labile, suggesting that the mating system may be promiscuous (both males and females mating with more than one partner) and that sperm competition may occur. The similarity between the chronology of reproduction in Malawi, Kenya, and South Africa leads us to propose that sperm storage occurs at all three localities.