BACKGROUND & AIMS: Abdominal bloating is an extremely intrusive symptom of irritable bowel syndrome (IBS) that is not always accompanied by an increase in abdominal girth (distention), raising the possibility that these 2 features of the condition may not share a common pathophysiology. A number of mechanisms have been postulated for bloating and distention, but the role of visceral sensation, which is often abnormal in IBS, has not been previously investigated, and this study aimed to address this question. METHODS: Abdominal girth measured by ambulatory abdominal inductance plethysmography and bloating severity was recorded over 24 hours in 39 IBS-constipation (ages, 18-73 years) and 29 IBS-diarrhea patients (ages, 20-59 years) meeting Rome II criteria. Within 1 week, rectal sensory thresholds were assessed with a barostat using the ascending method of limits and tracking. RESULTS: IBS patients who suffered with bloating alone had lower thresholds for pain (P = .005), desire to defecate (P = .044), and first sensation (P = .07) compared with those who had concomitant distention irrespective of bowel habit. When patients were grouped according to sensory threshold, hyposensitive individuals had distention significantly more than those with hypersensitivity (P = .001), and this was observed more in the constipation subgroup. Static and dynamic compliance did not differ among any of the groups. CONCLUSIONS: The symptom of bloating alone is associated with visceral hypersensitivity, suggesting that the pathogenesis of bloating and distention may not be the same. Consequently, treatment approaches may have to be different, and measuring visceral sensation could have utility in choosing the right therapeutic modality.