ST. LOUIS -- The exorcism involving Jesuit priests at Saint Louis University, which inspired the best-selling book and iconic film, "The Exorcist", is the most well documented example of the ancient Catholic ritual. While still extremely rare, exorcisms are still performed today.

In fact, every Catholic diocese in the United States has a designated exorcist.

"Before they agreed to perform the exorcism (in St. Louis in 1949), they made sure that the boy had been examined by medical personnel; psychiatrists, psychologists, medical doctors," explains SLU archivist David Waide. "It's not something that's taken lightly. It wasn't taken lightly in 1949 and it's certainly not something that's taken lightly in 2012."

Even though the ritual has been made famous by Hollywood, the number of Catholic priests trained to perform an exorcism has been falling in recent years. In fact, the Catholic church hosted a closed-door seminar in Baltimore two years ago to train more of the Catholic ranks in the methods of exorcism.

Some of the prayers used in an exorcism are one familiar to any Catholic, like the "Our Father". Others use language and phrases you might expect if you've seen movies dealing with demonic possession.

Here's an example:

"I command you, unclean spirit, whoever you are, along with all your minions now attacking this servant of God, by the mysteries of the incarnation, passion, resurrection, and ascension of our Lord Jesus Christ, by the descent of the Holy Spirit, by the coming of our Lord for judgment, that you tell me by some sign your name, and the day and hour of your departure."

For obvious reasons, the Catholic church does not openly advertise the ritual of exorcism.

Whenever a new book or movie dealing with exorcism comes out, Catholic officials hear from many mentally unstable people convinced they are possessed.

Many skeptics insist possession is a myth, and argue people showing the symptoms are actually suffering from multiple personality disorder.

For the Catholic church, an exorcism is a jurisdictional matter. The bishop, or archbishop, of a diocese has to approve the ritual and assign an exorcist "of mature years".

The 1949 case, in St. Louis, involved Jesuits at Saint Louis University but also required the approval of the Archdiocese of St. Louis at that time, Joseph Ritter.

The exorcism performed on the 13-year-old boy in St. Louis, a child referred to as "Robbie" in most accounts, happened primarily in three locations: at the boy's relative's home in North St. Louis County, at the rectory behind the College Church on the campus, and at a now-demolished wing of the old Alexian Brothers Hospital in South St. Louis.

Both the rectory behind the college church and the psychiatric ward at Alexian Brothers are no longer standing. Even so, SLU students throughout the years insist there are mysterious locked rooms on campus at DuBourg Hall and Verhagen Hall that were used to free the boy from the grip of Satan.

"It's just not true," says David Waide, SLU archivist.

One location where some of the exorcism happened is still standing. The home of the boy's relatives in north St. Louis County.

Thursday morning on Today in St. Louis, you will hear from the next door neighbors of that home. One of those neighbors, who sleeps with Holy Water near her bed, has a connection to the story that dates all the way back to 1949.

KSDK