Research suggests that autism may result from environmental factors that act during prenatal development. One idea is that a pregnant woman's diet could influence prenatal brain development, perhaps in a way that increases autism risk. Relatively little research has been dedicated to understanding how maternal dietary factors could influence brain development in offspring. One interesting dietary factor is intake of omega-3 fatty acids, which are found in fish and nut oils; these fatty acids may act in the brain to promote neural growth. Dr. Santagelo's fellow will determine whether women with low intakes of omega-3 fatty acids during pregnancy have increased risk of having a child with autism. The women studied will be from The Nurses' Health Study II cohort, a large cohort of over 100,000 female United States nurses who have been followed prospectively since 1989. The information collected on this group includes medical, obstetrical, and prospectively collected dietary factors, including omega-3 fatty acid intake. In 2005, over 800 women in the cohort reported having had a child with an autism diagnosis. This study will compare omega-3 fatty acid intakes in women with children with autism to the intake of women without children with autism in order to characterize the relationship between maternal diet and risk of autism. What this means for people with autism: This study may specify a prenatal environmental factor that influences autism risk, help prevent new cases, and define new treatment approaches.