The clinical assessment and investigation of irritable bowel syndrome would be greatly facilitated by the introduction of a simple, easy to use severity scoring system. Such a system, developed in our department over a number of years, has been submitted to validation in a total of 141 patients and 40 healthy controls. The system, incorporating pain, distension, bowel dysfunction and quality of life/global well-being, was assessed for its ability to reliably score patients previously classified as mild, moderate or severe. The reproducibility and sensitivity to change of the system was also assessed. The maximum achievable score was 500. Mild, moderate and severe cases were indicated by scores of 75 to 175, 175 to 300 and > 300 respectively. Controls scored below 75 and patients scoring in this range can be considered to be in remission. There was a highly significant difference between controls and patients as a whole (P = 0.0001) as well as significant differences (P < 0.01) between all severity categories. Scores repeated within 24 h were very reproducible and sensitivity to change was also extremely good (P < 0.001) with a change of 50 reliably indicating improvement. These results suggest that this scoring system should prove to be a valuable instrument in helping to meet the many challenges offered by irritable bowel syndrome.