Visceral hypersensitivity is often considered to play a major etiologic role in the pathophysiology of irritable bowel syndrome in adults, and some authors argue that this increased sensitivity is mainly due to psychological factors. In contrast, there are no data in children with irritable bowel syndrome which confirm this relationship. The aim of the study was to evaluate the relationship between psychosocial aspects and sensorymotor function in children affected by irritable bowel syndrome. Ten children fulfilling the Rome II criteria for irritable bowel syndrome and seven healthy controls were enrolled. We studied the thresholds and the perception of visceral stimuli in the rectum by means of an electronic barostat (isobaric phasic distentions, 3 mmHg/1 min, interval 1 min) and a validated questionnaire. Personality features were evaluated by means of the Big Five Questionnaire for Children. Sleep, mood disturbance, anxiety and individual performance (missed school days, school results and social activities) were also evaluated. Children with irritable bowel syndrome showed significantly lower thresholds for discomfort (14.8 +/- 3.5 vs 22.3 +/- 6.9 mmHg, P = 0.010) and a higher cumulative perception score (28.2 +/- 11.1 vs 12.3 +/- 8.0, P = 0.005) compared with healthy controls. A higher emotional instability (57.8 +/- 7.0 vs 48.7 +/- 10.1, P = 0.047), sleep disturbance (7.2 +/- 1.0 vs 9.3 +/- 0.5, P = 0.004) and anxiety (6.3 +/- 2.0 vs 2.3 +/- 1.7, P = 0.009) were observed in irritable bowel syndrome patients. Moreover, in a multivariate analysis, the cumulative perception score was significantly related to emotional instability (P = 0.042). In conclusion children with irritable bowel syndrome exhibit visceral hypersensitivity and psychosocial impairment. Emotional instability, as a personality feature in these children, seems to modulate the perception response to visceral stimulations.