Brown bear (Ursus arctos) food habits were examined from 1,500 fecal samples collected between 1974 and 2004 in the Cantabrian Mountains of northern Spain. The most important food items were graminoids and forbs in the spring, fleshy fruits (especially bilberries) in the summer, and hard mast in the autumn and winter (especially acorns). Animal matter also was consumed throughout the year. We found differences between 3 brown bear population nuclei within the Cantabrian population, which could be of enormous interest for habitat management. We also investigated how much interannual variation in different food items influenced our diet estimates. High fluctuations among years rather than values around a mean were inherent to some food items. However, for other items, the mean seems to be a reliable descriptor. We found that the additional years of data increased the coefficient of variation associated with some of our diet estimates and suggest the existence of directional changes in brown bear food habits that have been largely neglected. Although some studies suggest that diet is fixed and not changeable, our results show that long-term diet studies may reveal changes in habitat use patterns or habitat composition for brown bears and other wildlife species. Thus, incorporating diet studies into monitoring protocols can be helpful for designing and evaluating both current and future management actions.