Open-minded and structured interviews were conducted to assess post-traumatic stress disorder (PTSD) and other psychosocial outcomes among 24 men who had participated in the military's mustard gas testing program during World War II. Most men had volunteered (92%) and had participated in chamber tests (96%). During the tests, few (22%) understood the danger involved. The majority (67%) were ordered to refrain from discussing their participation with anyone. Most men (83%) experienced physical symptoms subsequent to the test. At present, the men were less psychologically and physically healthy than expected for men of similar age. The current prevalence of PTSD due to the mustard gas was 17%. The current prevalence of subdiagnostic mustard-gas-related PTSD was 25%. Lifetime estimates for full and subdiagnostic PTSD was 17 and 33%, respectively. The only mustard gas experience that predicted lifetime full or subdiagnostic PTSD was the number of exposures to the gas.