Background. In this study we examined the prevalence rates of post-traumatic stress disorder (PTSD), types of trauma most often associated with PTSD, the co-morbidity of PTSD with other lifetime psychiatric disorders, which disorders preceded PTSD, and gender differences in PTSD and trauma exposure in a representative sample of Chileans. Method. The DSM-III-R PTSD and antisocial personality disorder modules from the Diagnostic Interview Schedule (DIS) and modules for a range of DSM-III-R diagnoses from the Composite International Diagnostic Interview (CIDI) were administered to a representative sample of 2390 persons aged 15 to over 64 years in three cities in Chile. Results. The lifetime prevalence of PTSD was 4·4% (2·5% for men and 6·2% for women). Among persons exposed to trauma, rape was most strongly associated with PTSD. Onset of PTSD significantly increased the risk of developing each of the 10 other tested disorders. Among those exposed to trauma, women were significantly more likely to develop PTSD, after controlling for assaultive violence. Conclusions. This study highlights the importance of investigating the prevalence of PTSD, patterns of co-morbidity of PTSD, and gender differences in PTSD in non-English-speaking countries.