Introduction. The objective of this study is to validate a version in Spanish of the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). Method. We administered to 20 patients with obsessive-compulsive disorder (OCD) the Maudsley Obsessive-Compulsive Inventory (MOI) and a version in Spanish of the Y-BOCS. The application of the last one was performed by an «interviewer», filmed, and then watched and rated by other 4 «observers». In addition, the opinion of the treating psychiatrist about the severity of the patient's symptoms was registered. The interviewer and the observers were named «raters». Results. The mean scores of the Y-BOCS assigned by the 4 observers were from 18.35 to 19.55; the maximum scores, from 34 to 35; and the minimum scores, from 1 to 5. The Pearson's correlations between raters were significant for all cases (r>0.86 and p<0.001). For all raters, Y-BOCS scores significantly correlated with MOI scores (p<0.001) and the opinion of the treating psychiatrist (p<0.05). We did not find significant correlation between the last one and MOI scores. The Cronbach's coefficients ranged from 0.8789 to 0.9488. Conclusions. The Spanish version of the Y-BOCS is reliable, homogeneous and valid for quantification of the obsessive-compulsive symptoms, and has more correlation with the opinion of the treating psychiatrist than the MOI.