During the Middle Ages, demonic possession constituted an explanation for an erratic behavior in society. Exorcism was the treatment generally applied to demoniacs and seems to have caused some alleviation in the suffering of mentally distressed people. We have selected and analyzed some cases of demonic possession from thirteenth-century hagiographical literature. In the description of demoniacs we have been able to find traits of psychotic, mood, neurotic, personality disorders and epilepsy. The exorcisms analyzed in our article are the result of literary invention more than the description of a contemporary event. Nevertheless, the writers were witnesses of their time, transferred their knowledge about exorcism and possession in their narrative and presumably incorporated their actual experience with demoniacs.