With the aim of improving end organ treatment, we describe a new system of classifying irritable bowel syndrome (IBS) according to clinical features into four groups, spastic colon syndrome (SCS), functional diarrhea (FD), diarrhea-predominant spastic colon syndrome (DPSCS), and midgut dysmotility (MGD). The aim of the study was to investigate fasting and postprandial distal colonic motility in the four groups of patients and to compare the results with normal controls. Distal colonic motility studies were performed in the unprepared colon. 2.5-hr recordings were made from four channels with a standard meal administered at 0.5 hr. The intubated colon was treated as a study segment and data analyzed for study segment activity index (SSAI) and number and mean amplitude of pressure peaks over 30-min epochs. Patients with SCS had significantly higher (P < 0.05) mean amplitude of pressure peaks (60 min, 120 min) and SSAI (120 min) than controls and patients with FD, DPSCS, and MGD. In contrast, patients with FD and DPSCS had significantly (P < 0.05) lower postprandial SSAI than controls and patients with SCS (60 min, 120 min). With the exception of raised postprandial mean amplitude of pressure peaks (120 min), MGD patients had normal distal colonic motility. Division of IBS patients into subgroups has highlighted significant differences in distal colonic motility that provide insights into etiopathogenesis and should assist targeting of current and newly developed therapies, particularly receptor active agents.