Posttraumatic stress disorder (PTSD) is characterized by traumatic memories that can manifest as daytime recollections, traumatic nightmares, or flashbacks in which components of the event are relieved. These symptoms reflect excessive retrieval of traumatic memories that often retain their vividness and power to evoke distress for decades or even a lifetime. We have reported previously that elevated glucocorticoid levels inhibit memory retrieval in animals and healthy human subjects. We therefore hypothesized that the administration of cortisol might also inhibit the retrieval of traumatic memories in patients with PTSD. In a recent pilot study, we found the first evidence to support this hypothesis. During a 3-month observation period, low-dose cortisol (10 mg/day) was administered orally for 1 month to three patients with chronic PTSD using a double-blind, placebo-controlled, crossover design. In each patient investigated, there was a significant treatment effect with cortisol-related reductions in one of the daily rated symptoms of traumatic memories without causing adverse side effects. Future studies with more patients and longer treatment periods are required to evaluate the efficacy of cortisol treatment for PTSD.