Despite the importance of sharks to marine ecosystems as top predators and growing concern over the conservation status of many shark species, surprisingly little is known about many aspects of their reproduction patterns and life history. Better knowledge of breeding biology and reproductive parameters will be important for designing appropriate management plans to protect dwindling populations of sharks. Here, we report new information regarding the mating system and reproductive cycle of a large coastal shark, the lemon shark Negaprion brevirostris, revealed through field observations and genetic analyses of an adult female and her offspring. Our findings demonstrate that this female exhibited philopatry to a nursery ground in Bimini, Bahamas, where she returned to give birth in both 1996 and 1998. Genetic analyses using DNA microsatellite loci developed for lemon sharks provided the first demonstration of polygamous mating and multiple paternity in a carcharhinid shark; at least three males had sired the litter she delivered in 1998.