The humpback smooth-hound shark (Mustelus whitneyi) is one of the most captured shark species in the south-east Pacific and is classified as vulnerable, yet its reproductive biology has been poorly studied. The aim of this study was to increase our knowledge of the reproductive biology of the humpback smooth-hound shark. In all, 41 pregnant females, 386 macroscopically visible embryos in utero and 16 neonates were sampled off northern Peru. Pregnant females measured between 73- and 118-cm total length (TL) and the number of embryos per litter ranged from 6 to 18, with a mean of 10. Size at birth ranged between 21 and 22 cm TL. Litter size increased with the TL of the mother, yet this relationship was not strong (r2 = 0.36). The gestation period had a minimum duration of 7 months and a synchronous cycle in which birth occurred in September. The humpback smooth-hound shark is a placental viviparous elasmobranch. This study represents the most comprehensive research of the reproductive biology of the humpback smooth-hound shark, and is the first time the embryonic development is described for this species. These findings could contribute to the design and implementation of local management plans for this species.