Objective There is no objective means to assess the obstructed defaecation syndrome (ODS), to allow evaluation of outcome or to compare the efficacy of treatment including surgery. The study aimed to validate a disease-specific index to quantify severity to allow assessment of the results of treatment in clinical trials, to permit comparison between them. Method Seventy-six patients with ODS and 30 healthy controls entered the study after proctologic and ano-rectal physiological investigation. Hirschsprung's disease and slow transit constipation were excluded. An eight-item questionnaire with four or five possible answers was administered by two independent researchers at two different times. The ODS score was the sum of all points with a maximum possible of 31 points. Agreement between the two operators was evaluated by the Kappa coefficient for each single item. The coefficient of repeatability (CR) was assessed by the Bland and Altman plot. The internal consistency was evaluated by the Crohnbach-alpha test. A cluster analysis was carried out on each clinical finding. The Mann-Whitney U-test was used to compare median ODS score between patients and controls. Results The ODS score of the two operators was normally distributed and strongly correlated (r = 0.89). The correlation coefficient between the score assigned to each item by two operators ranged from 0.79 to 0.98. The degree of agreement between the operators was good and the two methods were reproducible (CR = 3.13). There was a significant difference between the mean ODS score for patients and controls (t = 20.70, P