Celiac disease is a genetic autoimmune disorder characterized by a heightened sensitivity to gluten, the protein in wheat, barley and rye. The disease is more common than most people think, affecting approximately 3 million in the United States, about 1 in 100. One of the most notable things about celiac disease is that up to 97 percent of Americans who have it remain undiagnosed. Awareness of the disease in the United States is increasing but it can still take years--an average of nine, according to Peter H.R. Green, MD, director of the Celiac Disease Center at Columbia University--to be diagnosed. This may be due to the fact that celiac disease can present with a wide range of subtle to serious symptoms that can vary from person to person. In this article, the author outlines what one should know about celiac disease.