This article is from the Tibet FAQ, by Peter Kauffner Peter.Kauffner@bearsden.org and Nima Dorje firstname.lastname@example.org.
The Chinese Communists put a great deal of emphasis on the ritual use of
human body parts in Tibetan Buddhism, especially with regard to human skulls
and thigh-bones. It is implied that these body parts were obtained by human
sacrifice -- an idea firmly rejected by scholars of Tibetan culture.
Another version of the human sacrifice charge is that Tibetans would
commonly, "bury living boys beneath important buildings or images, so that
they would `stand forever.'" It appears that this version is also
uncollaborated by independent scholarship. Perhaps this claim has it's origin
in the occasional Tibetan practice of burying bodies in the walls of houses.
Human sacrifice was a part of pre-Buddhist Tibetan tradition and there are
reports which suggest that it was occasionally practiced in more recent
times. [Grunfeld2], [Epstein83]