This study examines the epidemiology of obsessive-compulsive disorder (OCD) using data from the National Comorbidity Survey Replication (NCS-R), a nationally representative survey of U.S. adults. The findings reveal that over a quarter of respondents reported experiencing obsessions or compulsions at some point in their lives, but only a small proportion met full DSM-IV criteria for lifetime (2.3%) or 12-month (1.2%) OCD. OCD is associated with significant comorbidity, including anxiety and mood disorders, impulse-control disorders, and substance use disorders. The severity of OCD, assessed by the adapted Yale-Brown Obsessive Compulsive Scale (Y-BOCS), is linked to poor insight, high comorbidity, role impairment, and the likelihood of seeking treatment. The high prevalence of subthreshold OCD symptoms suggests that the public health burden of OCD may be greater than its low prevalence indicates. The study also highlights the importance of early-onset cases in males and the need for further research on the classification and heterogeneity of OCD in the DSM-V.This study examines the epidemiology of obsessive-compulsive disorder (OCD) using data from the National Comorbidity Survey Replication (NCS-R), a nationally representative survey of U.S. adults. The findings reveal that over a quarter of respondents reported experiencing obsessions or compulsions at some point in their lives, but only a small proportion met full DSM-IV criteria for lifetime (2.3%) or 12-month (1.2%) OCD. OCD is associated with significant comorbidity, including anxiety and mood disorders, impulse-control disorders, and substance use disorders. The severity of OCD, assessed by the adapted Yale-Brown Obsessive Compulsive Scale (Y-BOCS), is linked to poor insight, high comorbidity, role impairment, and the likelihood of seeking treatment. The high prevalence of subthreshold OCD symptoms suggests that the public health burden of OCD may be greater than its low prevalence indicates. The study also highlights the importance of early-onset cases in males and the need for further research on the classification and heterogeneity of OCD in the DSM-V.