Understanding population dynamics and historical declines for Mountain Goats (Oreamnos americanus) is challenging due to sparse data. Speculations regarding the cause of population declines have included habitat change, predation, disease, parasites, recreation impacts, and excessive harvest. Managing for recovery requires an understanding of the relative importance of the factors causing population declines. Using records of Mountain Goat harvest in selected areas of Washington State (USA), we modeled population trajectories for 7 areas with a stage-structured matrix model and compared these trajectories to recent population estimates. Our results supported the hypothesis that observed declines can be attributed primarily to the effects of harvest. We also assessed the level of harvest likely to be sustainable for Mountain Goat populations of varying sizes. Our results were sensitive to vital rates used in the model and were also influenced by population size and the proportion of harvest that is male. Generally, populations of <50 individuals should not be harvested, but larger populations (such as >100) or those where the proportion of males in the harvest is high (90 to 100%) may sustain ≤4% harvest. However, due to expected variation of vital rates among populations and years, declines may still occur with harvest at these levels and continued population monitoring is essential for hunted populations.