The majority of women who enter the criminal justice system, most of whom are poor and women of color, have suffered from significant lifetime trauma exposure that can lead to posttraumatic stress disorder (PTSD). It is essential to identify the prevalence of PTSD among this population in order to identify treatment needs. Most studies on PTSD among incarcerated women have focused on PTSD in jailed populations, including women awaiting trial. Using a cross-sectional study design, we estimated the prevalence of PTSD and comorbid physical and mental health conditions in 387 incarcerated women sentenced to a maximum-security prison in the United States. Almost half (44%) of our sample met the diagnostic criteria for PTSD. Women with moderate to severe PTSD symptoms were more likely to report several comorbid physical and mental health conditions than were women without PTSD. Women with the most severe symptoms were most likely to report receiving mental health treatment in prison; women with moderate to severe symptoms were less likely to report receiving similar mental health care. Our findings add support to the link between PTSD and comorbid physical and mental health conditions and suggest that many women with PTSD are not receiving mental health treatment that is likely to benefit them. Because prison has become the mental health safety net for some of the nation’s most vulnerable women, it is imperative that prisons provide evidence-based PTSD treatment during incarceration.