This study's goal was to develop a measure of late-onset stress symptomatology (LOSS). LOSS is a phenomenon observed in aging combat veterans who (a) were exposed to highly stressful combat events in their early adult years, (b) have functioned successfully throughout midlife with no history of chronic stress-related disorders, but (c) begin to register increased combat-related thoughts, feelings, and reminiscences commensurate with the changes and challenges of aging. Several samples of older male combat veterans from World War II, the Korean Conflict, and the Vietnam War served as participants. We developed a LOSS Scale that demonstrated a high degree of internal consistency reliability (coefficient alpha = 0.97). Scores were stable over brief intervals but were sensitive to developmental change over an extended period. Factor analysis suggested a single LOSS factor. Bivariate associations between LOSS score and other variables (e.g., indicators of contemporary life stressors, resilience, quality of life) were consistent with hypotheses, and there was support for the incremental validity of LOSS vis-à-vis posttraumatic stress symptoms and symptoms of general distress. Discussion of the potential uses of the scale, future directions for psychometric research, and suggestions for generalizing the LOSS construct to other trauma populations are provided.