Although case reports suggest the existence of a unique relationship between obsessive-compulsive disorder (OCD) and posttraumatic stress disorder (PTSD), results from large-scale epidemiological and clinical studies have been more equivocal. Furthermore, symptom overlap may artificially inflate the significance of the relationship between OCD and PTSD. Utilizing the Obsessive-Compulsive Inventory [OCI; Psychol. Assess. 10 (1998) 206] and the Posttraumatic Diagnostic Scale [PDS; Psychol. Assess. 9 (1997) 445], this study examined the relationship between OCD and PTSD symptoms in 128 patients diagnosed with OCD, 109 patients diagnosed with PTSD, 63 patients diagnosed with another anxiety disorder, and 40 college students. Experts in OCD and PTSD independently rated items on the OCI and PDS for the degree of overlap across the disorders. On the basis of these ratings, we created a scale from each measure that included only non-overlapping items. Results revealed that overall symptoms of OCD and PTSD were related in all samples. However, after controlling for depression and overlapping symptoms simultaneously, this relationship was no longer significant in the OCD and PTSD samples, although it remained significant in the anxious and college student comparison groups. These results support the presence of a relationship between symptoms of OCD and PTSD that may be largely accounted for by a combination of symptom overlap and depression.