Background: The risk of developing posttraumatic stress disorder (PTSD) among incarcerated women may be associated with drug use. Objectives: To establish the frequency of PTSD in a sample of incarcerated women and its relationship with drug use inside prison. Anxiety and depression, nature of stressors and sociodemographic data were evaluated and the sample of PTSD-positive women was compared with the one of PTSD-negative women. Methods: The study had a cross-sectional design. The PTSD was evaluated according to the DSM-IV criteria. Drug consumption was assessed with the Christo Inventory for drug consumption. Anxiety was evaluated with the Spielberger Inventory and depression with the Beck Inventory. Results: Among the 134 examined women, 40.3% showed PTSD. There was a significantly higher daily use of cocaine among women with a positive PTSD diagnosis (p < 0.01). Daily consumption of illicit drugs was reported by 53% of the assessed women in prison. Compared to PTSD-negative women, all participants diagnosed as PTSD-positive showed some degree of depression (p < 0.05). Discussion: The high prevalence of PTSD among incarcerated women is comparable to the prevalence of high-risk populations described in other studies. In spite of being in prison, consumption of illicit drugs was high. The association of PTSD with an increased cocaine use suggests a preference to consume stimulant drugs among incarcerated women with PTSD.