Hypotension, defined as systolic blood pressure less than 90 mm Hg, is recognized as a sign of hemorrhagic shock and is a validated prognostic indicator. The definition of hypotension, particularly in the elderly population, deserves attention. We hypothesized that the systolic blood pressure associated with increased mortality resulting from hemorrhagic shock increases with increasing age. The Los Angeles County Trauma Database was queried for all moderate to severely injured patients without major head injuries admitted between 1998 and 2005. Several fit statistic analyses were performed for each systolic blood pressure from 50 to 180 mm Hg to identify the model that most accurately defined hypotension for three age groups. The optimal definition of hypotension for each group was determined from the best fit model. A total of 24,438 patients were analyzed. The optimal definition of hypotension was systolic blood pressure of 100 mm Hg for patients 20 to 49 years, 120 mm Hg for patients 50 to 69 years, and 140 mm Hg for patients 70 years and older. The optimal systolic blood pressure for improved mortality in hemorrhagic shock increases significantly with increasing age. Elderly trauma patients without major head injuries should be considered hypotensive for systolic blood pressure less than 140 mm Hg.