Abdominal bloating is a relevant, troublesome, and poorly understood clinical problem. Despite its clinical importance, bloating remains substantially ignored, without proper clinical classification, known pathophysiology, and effective treatment. It is not even clear to what extent the complaints of individual patients correlate with objective evidence of abdominal distension, and this uncertainly regarding the subjective or objective origin of the complaints further adds to confusion. This article proposed a framework for investigating bloating, considering key factors potentially involved in its pathophysiology: distorted sensation, physical abdominal expansion, and abdominal wall dystony. Some data indicate that patients complaining of bloating have impaired transit and tolerance of intestinal gas loads. The problem does not seem to be too much gas, however, but rather abnormal responses to gas. Furthermore, abnormal control of abdominal muscle activity in these patients may contribute to objective distension. Bloating, like many other abdominal symptoms, probably represents a heterogeneous condition produced by a combination of pathophysiological mechanisms that differ among individual patients, resulting in a polymorphic clinical presentation. © 2005 Elsevier Inc. All rights reserved.