Large international studies on asthma and allergies in childhood have found notorious variation in prevalence and temporal trend among countries. However, there is no international studies on the epidemiologic characteristics of wheezing in the first year of life. The aim of this study was to validate a questionnaire to assess the prevalence of wheezing in infants from Latin America, Spain, and Portugal. This study was undertaken in pediatric emergency rooms (PER). A randomized sample of parents visiting PER because lower respiratory illness, answered a questionnaire on wheezing developed by the International Study of Wheezing in Infants. During visit, all infants were examined by one of the authors (blind) who reported, or not, the presence of wheezing on chest auscultation. Sensitivity, specificity, predictive positive value, predictive negative value, and agreement level were calculated from parent and physician reports. Two hundred and nine infants aged 12-15 months participated in the study. Fifty-six parents reported current wheezing and 43 were confirmed by physician; 153 parents did not report current wheezing and 146 had not wheezing at physical examination (agreement = 0.74, CI 95% 0.64-0.85). This questionnaire showed high sensitivity (86%), specificity (91.8%), positive predictive value (76.8%) and predictive negative value (95.4%). Regardless of previous experience with wheezing episodes, parents can reliably inform when their infants are currently wheezing. A simple and convenient questionnaire confirmed by physical examination produce an accurate tool to asses the prevalence of asthma symptoms in infants.