ABSTRACT: Blubber fatty acid (FA) profiles of young Steller sea lions Eumetopias jubatus (<24 mo old; n = 477) were investigated to determine whether regional, seasonal, age-class and sex differences occur in the diets of these demographic groups. Blubber FA profiles of spring (March to May) pups differed significantly by region, probably reflecting regional differences in the diet of adult females, who provide their pups with milk. While there were statistically significant seasonal and age-class differences in both Prince William Sound (PWS) and SE Alaska (SEA), differences in FA profiles between sexes were only evident in the blubber of yearlings from PWS. Within SEA, blubber FA profiles of summer pups differed significantly from all other seasonal/age-class groups in that region. This is consistent with movements of female–pup pairs from rookeries to haul-outs and hence differences in female foraging. In SEA, seasonal differences in blubber FA composition were evident and similar between yearlings and pups. In contrast, there was a gradual change in the FA profile of pup blubber from summer to spring in PWS, which did not follow the same seasonal pattern of yearling profiles. These differences in FA profiles suggest either differences in the timing of weaning between the 2 areas or shifts in the diets of lactating females, or both.