The New York Times > International > Middle East > Arafat's Death Remains a Mystery, Nephew Says After Seeing Records
And so the rumor mill goes. The most convincing theory I've heard is that he drank himself to death. It's less scandalous and more prosaic than the HIV theory, but it still explains why those in the know would want to keep the cause of his death secret. Alcohol consumption is forbidden to observant muslims.
I suspect the story will leak out over the next few months. If the bottle count was high I'd increase my confidence in the alcoholism therapy with secondary liver, cardiac and marrow failure. It's killed more than a few men Arafat's age.