Because functional bowel disorders have no reliable markers, they must be defined by their symptoms. The various constellations of symptoms (syndromes) may have different mechanisms, differential diagnoses, and treatments. Therefore, precise classification is important on clinical and scientific grounds. Functional bowel disorders are a subset of functional gastrointestinal disorders attributed to the intestine. By symptoms they may be subclassified as IBS, burbulence, functional constipation and functional diarrhea. "Orphan" symptoms insufficient to qualify as one of these syndromes may be classified as unspecified functional bowel disorder. There may be overlap in symptoms among the disorders. A more careful definition of these symptom complexes will permit a logical approach to their study, investigation, and management.