['To evaluate the accuracy of clinical assessment of adenoidal obstruction based on a standardized score of the degree of mouth breathing and speech hyponasality (nasal obstruction index [NOI]) in comparison to nasal fiberoptic endoscopy.', 'Cross-sectional study with planned data collection.', 'Outpatient clinics of the Departments of Maternal and Pediatric Sciences and Specialized Surgical Sciences, University of Milan, Italy.', 'Children aged three to 12 years with adenoidal obstruction suspected on the grounds of persistent/recurrent otitis media or perceived obstructive nasal breathing were eligible. Ear, nose, and throat examination, allergy testing, NOI measurement, and nasal fiberoptic endoscopy to assess the degree of adenoidal hypertrophy were performed. Agreement between the NOI and adenoidal hypertrophy grade was assessed in the patients as a whole and by clinical subgroups.', 'A total of 202 children were enrolled: 54.9 percent had otological diseases and 45.1 percent had perceived obstructive nasal breathing. Most of the children (79.2%) showed mild or moderate clinical nasal obstruction. Adenoidal hypertrophy ranged from no obstruction (18%) to severe obstruction (38%). There was no substantial agreement between the NOI and the degree of adenoidal obstruction in the population as a whole and in all the clinical subgroups. False positive findings were significantly more frequent among allergic children (50%) than non-allergic children (22.4%, P = 0.009).'] Is clinical assessment of adenoidal obstruction based on the nasal obstruction index no longer useful in children?