The overlap in definition and presentation between posttraumatic stress disorder (PTSD) and borderline personality disorder (BPD) has raised questions about the relationship of these disorders. Are they separate disorders, variants of the same disorder, or comorbid conditions? The present study examined etiological variables and current functioning among two groups of outpatient women with a history of childhood sexual abuse: those with PTSD only (N = 45) and those with PTSD and BPD (N = 26). The groups did not differ in severity, frequency, or number of perpetrators of their childhood sexual abuse, or whether the perpetrator was a family member or not. The additional diagnosis of BPD was associated with earlier age of abuse onset and significantly higher rates of physical and verbal abuse by mother. Severity and frequency of PTSD symptoms were not affected by BPD diagnosis, suggesting that the personality disorder and PTSD are independent symptom constructs. The PTSD+BPD group scored higher on several other clinical measures including anger, dissociation, anxiety, and interpersonal problems. They did not differ in their frequency of use of mental health services but tended to be less compliant in their treatment. These and other findings are discussed, and implications for treatment are considered.