A new, 90-page leather-bound manual, written in Latin, warns priests to undertake the exorcism ritual only if they are sure that the person is truly possessed by the Devil.
The document states that tell-tale signs for possession are "speaking unknown languages, showing a visceral aversion to God and physical strength disproportionate to their age and health". If in doubt, exorcists are advised to consult psychiatrists or psychologists.
Presenting the new manual for exorcists, Cardinal Jorge Medina Estevez said "simple people often confuse psychological or psychosomatic disturbances with problems of the Devil". However he warned that while the number of individuals really possessed by the Devil today was relatively small, the Prince of Darkness was still at large in society.
He said the Devil "fooled people into believing that happiness can be found in money, in power and in carnal lust" and part of his strategy was convincing people he didn't exist.
The Pope, who is reported to have carried out an exorcism at the Vatican in 1982, has frequently railed against Satan, calling him a "cosmic liar".
Psychiatric science is not the only element of 20th-century life that has forced the Vatican to issue new tips for those charged with driving out the Devil. Exorcists are also told to protect the privacy of their "patients" and the presence of the media at exorcisms is absolutely forbidden.
Despite the new advice on detecting the Devil's presence, the ritual itself is essentially unchanged from the sprinkling of holy water, the laying of hands, the use of the crucifix and the final pronouncement "Go Back, Satan".