OBJECTIVES: To identify childhood antecedents for lifetime post-traumatic stress disorder (PTSD) and to determine how this diagnosis relates to health and service use among extremely poor women. METHODS: We conducted a secondary data analysis of 425 women in the Worcester Family Research Project, a case-control longitudinal study of 220 sheltered homeless and 216 extremely poor housed (never homeless) women in Worcester, Massachusetts. RESULTS: We found that extremely poor women with lifetime PTSD were more likely to have grown up in family environments of violence, threat, and anger than those without PTSD. The strongest risk factor for PTSD was childhood sexual abuse with threat. Low-income women with lifetime PTSD had more bodily pain, even when controlling for other health and demographic factors. Women with PTSD experienced more chronic health conditions and had more problematic relationships with their health care providers and perceived more barriers to care. CONCLUSION: Many low-income women have difficulty using medical care appropriately because of childhood histories of physical and sexual abuse, the subsequent development of post-trauma responses, and structural barriers to care. Given these factors, it is critical that health care clinicians routinely screen for histories of violence and PTSD and develop treatment plans that ensure safety, link current symptoms with prior experiences, and provide support as necessary. A team approach coordinated by a case manager may be the best strategy. Without routine screening for PTSD and sensitive treatment, many extremely poor women will receive compromised health care and may even be retraumatized.