The definition of asthma has always been a matter of discussion. The European Community Respiratory Health Survey (ECRHS) is a multinational survey designed to compare the prevalence of asthma in subjects aged 20 to 44 years throughout European countries. In each center a representative sample completed a self-administered screening questionnaire composed of nine dichotomous items. We propose a method for constructing a score for the ECRHS screening questionnaire and we validate the method with reference to the clinical diagnosis available for the Italian centers. Clinical diagnosis was made by a group of medical experts after examining the responses to a standardized clinical interview, respiratory function tests, and allergy tests. Before constructing a summary score, the number of latent factors/dimensions explaining correlations among the observed items was recognized. We identified only one factor/dimension underlying the screening questionnaire, so a summary score was determined by the Homogeneity Analysis by Alternating Least Square (HOMALS). Using best Receiver Operating Characteristic (ROC) threshold the diagnostic test of the score had sensitivity and specificity of 75.1 and 80.1%, respectively. The method of scoring is easily reproducible, and has the advantage of optimizing information recoded by the questionnaire.