In cetaceans almost all the energy reserves in lipid form are allocated to blubber and are related to basal metabolism and thermal insulation. Our study analyzed the blubber of 57 specimens of franciscana (Pontoporia blainvillei) from the state of Rio Grande do Sul, Brazil. Body fat condition was estimated through blubber weight, girth, and thickness of blubber. Blubber weight increased along with growth, from 2.27 kg in calves to 8.86 kg in mature franciscanas. Blubber weight decreased from 33.91% of total weight in calves to 24.32% in mature franciscanas. A significant difference was found when age classes were compared to each other (P < 0.001) for both males and females, indicating that blubber varied according to growth, independent of sex. Girth showed a good correlation with blubber weight at all 6 locations where it was measured, and thickness of blubber presented a low correlation at all 19 locations where it was measured. Calves face the physiologic problems of low surface to volume ratio, whereas adults expend energy in feeding, reproduction, and taking care of calves.