Our aim was to compare rectal perception of patients with diarrhea-predominant irritable bowel syndrome (IBS-D), constipation-predominant irritable bowel syndrome (IBS-C), functional constipation (FC), and healthy controls and to evaluate the therapeutic effect of acupoint transcutaneous electric nerve stimulation (TENS). Age- and sex-matched patients (24 IBS-D, 20 IBS-C, and 30 FC) were selected, and 30 volunteers served as healthy controls. Rectal sensory thresholds were evaluated by rectal balloon distension. Short- and long-term acupoint TENS was given respectively. IBS-D patients had significantly lower rectal sensory thresholds of the first sensation of stool, urgency of defecation, and pain than IBS-C or FC patients or healthy controls (P < 0.05), but there were no differences in rectal sensory thresholds among IBS-C and FC patients and healthy controls. In each group, females had significantly lower rectal sensory thresholds than males (P < 0.05), but there was no difference between younger (< or = 50 years old) and older (> 50 years old) patients. Short-term acupoint TENS increased rectal sensory thresholds of IBS-D patients. After 2-month acupoint TENS treatment in IBS-D patients, rectal sensory thresholds were significantly increased, stool times and the intensity of abdominal pain were decreased, and psychological scores were relieved to normal. Lowered rectal perception threshold is a hallmark of IBS-D patients. Females have significantly lower rectal sensory thresholds than males. Acupoint TENS is effective to treat IBS-D.