We assessed structure, survival, productivity, and growth of a Bison bison population in southern Utah during 7 years. Consistently female-biased sex ratios resulted from male-biased hunting mortality and possibly from lower survival of young males. Survival, excluding hunting mortality, was high for all animals and probably was facilitated by a lack of predators and by prolonged parental care of young. Productivity was correlated nonlinearly with precipitation and was lower than in other herds, possibly because of relatively sparse forage. The herd has been increasing exponentially since establishment in the early 1940's, despite annual hunts, low forage production, and possible competition with domestic cattle. Increase has been particularly rapid during an extraordinary series of relatively wet years since the drought of 1977, raising the question of whether the herd has exceeded long-term carrying capacity.