Cyclic vomiting syndrome (CVS) is a rare disorder characterized by recurrent episodes of severe nausea and vomiting. An episode may last for a few hours to several days and then is followed by a period of time during which affected individuals are free of severe nausea and vomiting. This alternating pattern of disease and disease-free periods distinguishes cyclic vomiting syndrome from other similar disorders. The associated nausea and vomiting can be severe enough to be incapacitating (e.g., individuals may be unable to walk or talk and/or be bedridden). Additional symptoms that are often present during an episode including paleness of the skin (pallor), lack of energy (lethargy), abdominal pain and headaches. In some cases as children grow older, they may outgrow these episodes, although many of these children eventually develop migraines. Cyclic vomiting syndrome affects children more often than adults. In adults, episodes occur less frequently, but may last longer. The exact cause of cyclic vomiting syndrome is unknown.