This study assessed the prevalence and interrelationships of posttraumatic stress disorder (PTSD), antecedent trauma, and psychosocial risk factors among pregnant women served at three urban Federally Qualified Health Care Centers. This analysis was part of a validation study of the prenatal risk overview, a structured psychosocial risk screening interview. The study sample included 745 prenatal patients at three clinics who also were administered the major depression, PTSD, alcohol, and drug use modules of the Structured Clinical Interview for DSM-IV (SCID). Most participants were women of color (89.1%), under the age of 25 years (67.8%), and unmarried (86.2%). The rate for a current PTSD diagnosis was 6.6% and for subthreshold PTSD 4.2%. More than half (54%) of participants reported a trauma that met PTSD criteria; 21% reported being a victim of or witness to violence or abuse, including 78 % of women with PTSD. Compared to those without PTSD, those with PTSD were 4 times more likely to be at risk for housing instability (AOR 4.15; 95% CI 1.76, 9.80) and depression (AOR3.91; 95% CI 2.05, 7.47) and 2 times as likely to be at risk for a drug use disorder (AOR 1.96, 95% CI 1.04, 3.71) and involvement with child protective services (AOR 2.27; 95% CI 1.06, 4.89). Women age 25 or older were twice as likely to meet PTSD diagnostic criteria as younger women (AOR2.27; 95%CI 1.21, 4.28). Trauma exposure and pervasive PTSD were common in this population. Systematic psychosocial risk screening may identify the population with PTSD even without questions specific to this disorder.