The authors’ goal was to compare the efficacy of a manualized cognitive behavior therapy that addresses both posttraumatic stress disorder (PTSD) and substance abuse (seeking safety) with a manualized cognitive behavior therapy that addresses only substance abuse (relapse prevention) and with standard community care for the treatment of comorbid posttraumatic stress disorder (PTSD) and substance use disorder. One hundred seven women from an urban, low-income population who had comorbid PTSD and substance use disorder were randomly assigned to receive the two kinds of cognitive behavior therapy or received standard community treatment. Participants were recruited from both community and clinical populations and evaluated with structured clinical instruments. Forty-one women received seeking safety therapy, 34 received relapse prevention therapy, and 32 received standard community care. At the end of 3 months of treatment, participants in both cognitive behavior therapy conditions had significant reductions in substance use, PTSD, and psychiatric symptoms, but community care participants worsened over time. Both groups receiving cognitive behavior therapy sustained greater improvement in substance use and PTSD symptoms at 6-month and 9-month follow-ups than subjects in the community care group. Seeking safety and relapse prevention are efficacious short-term treatments for low-income urban women with PTSD, substance use disorder, and other psychiatric symptoms.