Previous work from the Tierney laboratory has suggested that some individuals with autism spectrum disorders (ASDs) have very low blood cholesterol levels. Low cholesterol may be an important marker for subtypes of ASD; it may also play a role in causing some types of ASD, as cholesterol is known to be important for several aspects of brain development. The present study will test the response of individuals with ASD and low cholesterol to increased cholesterol in their diets. A randomized sample of youths with ASD will be given supplementary cholesterol over a 12 week period, and the effects of the treatment on behavior, communication, and other features of autism will be measured and compared to a group given placebo. This research will help to determine whether adding cholesterol to the diet can improve behavioral problems seen in individuals with ASD and low cholesterol.