Post-traumatic stress disorder (PTSD) is characterized by disabling symptoms of re-experiencing, avoidance and numbing after a traumatic event. Increased awareness of the disorder in the United States occurred after the attack on the World Trade Center and Hurricane Katrina. In addition, PTSD is a common mental health condition of soldiers returning home from war. This study measures the prevalence of PTSD in primary care patients attending an urban university-affiliated hospital. The researchers examine both overall prevalence as well as prevalence among patients with seven specific conditions. A total of 607 patients, aged 18–65 years old, participated in the study. The researchers found among 509 patients in primary care, 23 percent had PTSD and 11 percent of those had the disorder noted in their medical record. In patients with certain conditions—pain, irritable bowel syndrome, depression, anxiety disorder and substance dependence—the disorder was two to three times as high as in those patients without the conditions. These patients accounted for more than 90 percent of all PTSD cases. An unexpected finding was a lower PTSD occurrence among immigrants. The researchers suggest developing and testing more screening tools and interventions for PTSD in a primary care setting.