We evaluated various measurements of mass, morphology, and blubber thickness as indices of fatness for Steller sea lions by correlation with the percentage of total body mass comprised by the sculp (%SCULP). We concluded LMD-index was the best index evaluated because it had a relatively high r2 (0.58), had a linear relationship with %SCULP, and the intercept term was not different from O. We suggest the development of a LMD-index for otariids would likely reduce the unexplained variation in the index. We developed a multiple regression model (r2= 0.745, P < 0.001) for predicting %SCULP with LMD-index and functions of sex, age, and season as predictor variables. Steller sea lions < 5 yr of age had higher %SCULP values than those ≥ 5 yr. %SCULP declined with age for sea lions < 5 yr. Both younger and older males were fatter during the winter/spring period than during summer/ fall. Females of both age classes had similar %SCULP values throughout the year. Steller sea lions are relatively lean pinnipeds; estimates of blubber and total body lipids ranged from 5% to 17% of total body mass.