"As I see it, the evidence for possession is like the evidence for George Washington’s crossing of the Delaware. In both cases, written historical accounts with numerous sound witnesses testify to their accuracy. In the end, however, it was not an academic or dogmatic view that propelled me into this line of work. I was asked to consult about people in pain. I have always thought that, if requested to help a tortured person, a physician should not arbitrarily refuse to get involved. Those who dismiss these cases unwittingly prevent patients from receiving the help they desperately require, either by failing to recommend them for psychiatric treatment (which most clearly need) or by not informing their spiritual ministers that something beyond a mental or other illness seems to be the issue. For any person of science or faith, it should be impossible to turn one’s back on a tormented soul."
Writes Richard Gallagher, a psychiatrist and a professor of clinical psychiatry at New York Medical College who is writing a book about demonic possession in the United States. Watch out, it's a WaPo link.
ADDED: The question of what is true is often superseded by what will help. In a sense, what helps is what's true. It's true that it helps (if it helps).