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As good condition sagebrush steppe continues to be lost, it becomes increasingly important to improve our understanding of the biology and ecology of big sagebrush (Artemisia tridentata). One of the less well understood aspects of the biology of sagebrush is its population ecology. Stand age structure, or demography, is one of the most basic measures used to understand the stand condition of woody plants. It has been suggested that big sagebrush stands can become decadent due to old age of the individuals within the population and that management action would be required to rejuvenate that stand. The potential for decadence due to old age can be revealed by examining the stand age structure. Few efforts to measure the stand age structure of big sagebrush have been reported. We selected 14 one-hectare plots in an area of primarily Wyoming big sagebrush (A. t. wyominensis) that appeared to represent a broad range of sagebrush size, density, cover, and condition. From each plot we collected stem cross sections from approximately 70 total individuals of big sagebrush; including approximately 50 live and 20 dead sagebrush stems. Growth rings on each cross section were counted to determine age of live shrubs and age at death for dead shrubs. The overall average age of the 636 cross sections of live sagebrush was 14.9 years. Mean age per plot ranged from 7.3 to 22.6 years. Maximum ages of live sagebrush ranged from 22 to 86 years. Only 7% of the individuals sampled were two years old or less. Mean age at death ranged from 25.9 to 49.4 years. All plots had uneven stand age distributions indicating that all plots were experiencing ongoing, periodic recruitment events. The stand age distributions observed do not suggest big sagebrush stands might become decadent due to old age.