- CONTEXT: Heightened moral sensitivity seems to characterize patients with obsessive-compulsive disorder (OCD). Recent advances in social cognitive neuroscience suggest that a compelling relationship may exist between this disorder-relevant processing bias and the functional activity of brain regions implicated in OCD. OBJECTIVE: To test the hypothesis that patients with OCD demonstrate an increased response of relevant ventromedial prefrontal and orbitofrontal cortex regions in a functional magnetic resonance imaging study of difficult moral decision making. DESIGN: Case-control cross-sectional study. SETTING: Hospital referral OCD unit and magnetic resonance imaging facility. PARTICIPANTS: Seventy-three patients with OCD (42 men and 31 women) and 73 control participants matched for age, sex, and education level. MAIN OUTCOME MEASURES: Functional magnetic resonance imaging activation maps representing significant changes in blood oxygenation level-dependent signal in response to 24 hypothetical moral dilemma vs nondilemma task vignettes and additional activation maps representing significant linear associations between patients' brain responses and symptom severity ratings. RESULTS: In both groups, moral dilemma led to robust activation of frontal and temporoparietal brain regions. Supporting predictions, patients with OCD demonstrated significantly increased activation of the ventral frontal cortex, particularly of the medial orbitofrontal cortex. In addition, the left dorsolateral prefrontal cortex and left middle temporal gyrus were more robustly activated in patients with OCD. These results were unexplained by group differences in comorbid affective symptoms. Patients' global illness severity predicted the relative magnitude of orbitofrontal-striatal activation. The severity of "harm/checking" symptoms and "sexual/religious" obsessions predicted the magnitude of posterior temporal and amygdala-paralimbic activation, respectively. CONCLUSIONS: The neural correlates of moral sensitivity in patients with OCD partly coincide with brain regions that are of general interest to pathophysiologic models of this disorder. In particular, these findings suggest that the orbitofrontal cortex together with the left dorsolateral prefrontal cortex may be relevant for understanding the link between neurobiological processes and certain maladaptive cognitions in OCD.