IBS is a functional gastrointestinal disorder, a condition in which symptoms are due to dysfunction of the gut, not a structural problem like cancer. Nevertheless it is a real and treatable medical condition. IBS is a chronic disorder that is characterized by recurring (symptoms that come and go over time) abdominal discomfort or pain associated with an altered bowel habit, either constipation, diarrhea or both. IBS is different from routine, occasional constipation or diarrhea. IBS is best defined by what it is NOT: Know the facts.