In order to study the distribution and abundance of Strombus costatus, larvae and adults, samples were collected bimonthly from August 1997 to July 1998 at six sites at Banco Chinchorro. To collect larvae, replicate surface plankton tows were made with a conical net. Larval density ranged from 0.0018[plus or minus]0.026 veligers/10 m3 to 4.77[plus or minus]3.50 veligers/10 m3. Presence of all larval stages suggested a complete development of veligers from egg stage to metamorphic competence in the reef lagoon; 8.52% of the larvae corresponded to stage II veligers, 18% to stage III and 72.65% to stage IV. At the bottom, all conch found within three 100-m2 replicate areas were counted, shell lengths were measured and egg masses recorded. Conch density varied from 0.0025 to 0.22 conch/m2 with a dominance of juveniles. The total population in Banco Chinchorro was estimated at 1.3[x]106 conch, but only 8% were estimated to be of legal size. Larvae and adults were more abundant in Cayo Centro, the principal distribution site. Egg masses were abundant from May to October with a greater abundance in May. Banco Chinchorro is an important source of S. costatus veligers and sustains an adult and juvenile population within the reef lagoon. Nevertheless, this S. costatus population is not large enough to support a commercial fishery. It is necessary to protect the reproduction sites to maintain larval supply downstream. Inglés