Once upon a time a fussy baby was labeled with "colic," which is really a five-letter word for "the doctor doesn't know why." New insights into the cause of colicky behavior and frequent, painful nightwaking episodes reveal that oftentimes babies hurt because of some underlying medical problem. In fact, in our practice we have replaced the term "colicky baby" with "the hurting baby," which motivates the parents and the doctor to keep searching for the cause. One of the most common hidden medical causes of colic is a condition known as gastroesophageal reflux (GER), in which irritating stomach acids are regurgitated into the esophagus causing pains that adults would call "heartburn." GER is caused by a malfunction of the valve- like muscles between the stomach and the esophagus. Besides triggering colicky behavior, GER is a subtle cause of unexplained bouts of wheezing or asthma in infants and children.