Objective : Several reports have found abnormal levels of androgen in post-traumatic stress disorder (PTSD) patients. This abnormality in androgen is hypothesized to due to chronic psychological stress effects on the hypothalamic-pituitary-gonadal (HPG) system. The present study was conducted to estimate serum testosterone levels in PTSD patients in comparison with normal subjects. Methods : Seventy-five male Korean veterans of the Vietnam War volunteered for the study, of which eleven were excluded because of incomplete psychological assessment. To measure basal serum testosterone, blood samples were collected between 8.00 and 9.30 a.m. The clinician administered PTSD scale (CAPS), the structured clinical interview for DSM-IV (SCID), Hamilton Anxiety Rating Scale (HAM-A), Hamilton Rating Scale for Depression (HAM-D), Mini International Neuropsychiatric Interview Plus (Korean version of MINI-Plus), CES-K (Korean version of combat exposure scale). Results : The serum testosterone level of PTSD patients ($5.4{pm}2.5ng/mL$) was higher than that of a control group ($3.1{pm}1.7ng/mL$, p<0.001). Testosterone levels were significantly correlated with CAPS (r=.38, p<.01), HAM-A (r=.35, p<.01) and HAM-D (r=.28, p<.01) in all subjects. Conclusion : The results of the present study suggest that chronic psychological stress affects the HPG system.