The von Bertalanffy growth model was applied to franciscana dolphins (Pontoporia blainvillei) incidentally caught in fishing nets on the São Paulo/Paraná coasts (25°00′–25°58′S), and compared with the growth of franciscanas incidentally caught on the Rio Grande do Sul coast (29°–33°S). In both locations, a difference was noted between the growth of males and females, confirming the sexual dimorphism of the body proportions of this dolphin. The growth curves of the dolphins from São Paulo/Paraná were significantly different (P < 0.01) from those obtained from Rio Grande do Sul, with significantly smaller animals in the former area. On the São Paulo/Paraná coast, the stabilization of the growth curves happened at a total length of 113 and 129 cm for males (n= 23) and females (n= 18), respectively. In Rio Grande do Sul, they stabilized at 130 cm for the males (n= 59) and at 146 cm (n= 48) for the females. These results corroborate the morphometric differences previously mentioned in the literature, which resulted in the identification of a smaller northern form and a larger southern form of P. blainvillei. The data here presented can be used for future comparisons of changes in growth parameters of these two franciscana stocks and help to develop proper conservation programs for the species.