Prior research has indicated a seemingly unique relation between obsessive-compulsive disorder (OCD) and posttraumatic stress disorder (PTSD) that appears to relate to negative treatment outcome for OCD. However, to date, the prevalence of trauma and PTSD in individuals seeking treatment for OCD is unclear. To begin to address this gap, this study assessed history of traumatic experiences and current PTSD in individuals seeking treatment for treatment-resistant OCD. Trauma predictors of PTSD severity also were examined in this sample. Participants included 104 individuals diagnosed with treatment-resistant OCD who sought treatment over the course of 1 year from OCD specialty treatment facilities. Data were collected via naturalistic retrospective chart reviews of pre-treatment clinical intake files. Findings revealed that 82% of participants reported a history of trauma. Over 39% of the overall sample met criteria for PTSD, whereas almost 50% of individuals with a trauma history met criteria for PTSD. Interpersonal traumas and greater frequency of traumas were most predictive of PTSD severity, and individuals diagnosed with OCD and additional major depressive disorder (MDD) or borderline personality disorder (BPD) appeared at particular risk for a comorbid PTSD diagnosis. PTSD may be relatively common in individuals diagnosed with treatment-resistant OCD; and interpersonal traumas, MDD, and BPD may play a relatively strong predictive role in PTSD diagnosis and severity in such OCD patients.