Increasing attention has been paid to the possibility that a range of disorders, the putative obsessive-compulsive spectrum disorders (OCSDs), may share overlapping phenomenological and neurobiological features with obsessive-compulsive disorder (OCD). The development of a structured clinician-administered interview for the putative OCSDs (SCID-OCSD) is described. This instrument was used to investigate differences between OCD patients with a comorbid putative OCSD and OCD patients without a comorbid putative OCSD. A sample of 85 adult patients (38 men and 47 women) presenting for treatment of OCD was interviewed with the SCID-OCSD. OCD patients without comorbid putative OCSDs (n = 36) were compared to patients with comorbid OCSDs (n = 49) in terms of demographic features, clinical characteristics, and associated comorbidity with other non-OCSD DSM-IV axis I disorders. Of the OCD patients, 57.6% currently met criteria for at least one putative OCSD and 67.1% had a lifetime history of at least one comorbid OCSD. The OCSDs with the highest prevalence rates were compulsive self-injury (22.4%), compulsive buying (10.6%), and intermittent explosive disorder (10.6%). There was a significantly larger proportion of women in the group with comorbid OCSDs. Although the two groups did not differ in terms of severity of OCD symptoms, the group with comorbid OCSDs had significantly more obsessions and compulsions. The two groups did not differ significantly in terms of associated psychopathology other than OCSDs. We conclude that the SCID-OCSD provides clinicians and researchers with an instrument for the diagnosis of putative OCSDs. Our findings suggest that putative OCSDs have a relatively high prevalence rate in OCD patients. In addition, OCD patients with comorbid OCSDs differ with regard to certain demographic and clinical features. Further research, particularly genetic and neuroimmunological work, may ultimately be useful in validating the obsessive-compulsive spectrum.