Some well-researched books on the subject include "Fat and Cholesterol are good for you" by Uffe Ravnskov and "The Great Cholesterol con" by Anthony Colpo.

High levels are correlated with atherosclerosis and cardiovascular disease, but they haven't been shown to cause those conditions. Some cholesterols are also "good" (high density) in that they have positive effects for people with high cholesterols -- they can lower levels.