Conversion paralysis is characterized by a loss of voluntary motor functioning without an organic cause. Despite its prevalence among neurological outpatients, little is known about the neurobiological basis of this motor dysfunction. We have examined whether the motor dysfunction in conversion paralysis can be linked to inhibition of the motor system, or rather to enhanced self-monitoring during motor behavior. We measured behavioral and cerebral responses (with fMRI) in eight conversion paralysis patients with a lateralized paresis of the arm as they were engaged in imagined actions of the affected and unaffected hand. We used a within-subjects design to compare cerebral activity during imagined movements of the affected and the unaffected hand. Motor imagery of the affected hand and the unaffected hand recruited comparable cerebral resources in the motor system, and generated equal behavioral performance. However, motor imagery of the affected limb recruited additional cerebral resources in the ventromedial prefrontal cortex and superior temporal cortex. These activation differences were caused by a failure to de-activate these regions during movement imagery of the affected hand. These findings lend support to the hypothesis that conversion paralysis is associated with heightened self-monitoring during actions with the affected arm.