Denise is a 10-year-old girl who was admitted to the hospital for treatment of dehydration secondary to severe vomiting for 2 days. She was unable to retain any liquids. This was her 62nd admission for similar symptoms. These began when she was 5 years old. There was no family history of relatives with similar symptoms, but a paternal grandmother had severe migraine episodes for much of her life. Denise's parents were unable to determine what triggered Denise's vomiting episodes. At various times, they had restricted certain foods, focused on more regular sleep times for her, and assessed possible stressors in school, but the episodes seemed to occur at random times. The family lived on a farm, and their primary product was hogs. Denise was the second of four children. She was doing well in the fifth grade and was active in 4-H and in Sunday school. There were four living grandparents nearby, as well as many aunts, uncles, and cousins. There were frequent family get-togethers. At physical examination, Denise was irritable, spoke in monosyllables, and preferred to remain curled in a fetal position with her eyes closed. Her temperature was 98.8° F; her pulse was 120 beats per minute; her respiratory rate was 20; and her blood pressure was 85/60 mm Hg. Her eyes were slightly sunken. Her mouth was dry, and her skin appeared dry. Intravenous fluids were begun. After 24 hours, Denise was able to retain popsicles and sips of water. After 48 hours, she was ravenously hungry and was eating solids without difficulty. Her personality had changed dramatically. She was talkative, she laughed frequently, and she was discharged to home.