Do you mean the Mitchell-Hedges skull? Anna Mitchell-Hedges claimed she found it while assisting her father in one of his digs in Belize, but I personally don't believe that. She claimed that it possessed all sorts of mystical powers, and that it could not be reproduced by modern methods.
I remember watching a show on TV where they produced an exact replica of the skull (which rather undermines AMH's assertion) and then gave it to one of the forensic artist types who works out what a person's face would have looked like based on bone structure. The assumption being that the original skull's carver put so much detail in that they must have been intimately familiar with the biology of a human skull - basing their creation on real skulls they had seen. It is therefore somewhat odd that the skull has genetic markers that suggest it was based on the skull of a European woman.
There is further information here; http://www.archaeology.org/online/features/mitchel... from an anthropologist at the Smithsonian who has studied the original skull at a microscopic level and concluded that it was made using 20th century technology.