Background: The ability of a specific test to predict a difficult intubation is decreased by the variability of definitions of difficult intubation/laryngoscopy. The Mallampati classification system is a widely utilized approach for evaluating patients in the preoperative setting. Zero class of Mallampati is a new class of airway view that to add to the four modified Mallampati classes. This study estimates the incidence of class zero airway and determines the ability of Mallampati score, age and sex on the prediction of the larangoscopy grade.
Methods: This is a cross sectional study in which 376 patients aged 7-18 years and A.S.A physical status I or II were enrolled. They were scheduled for surgery under general anesthesia All the airway assessments were done in the sitting position, with the patient's head in neutral position, mouth fully open, tongue fully extended and without phonation. After induction of general anesthesia, laryngoscopy grade was assessed in sniffing position using the Cormak & Lehame grading scale.
Results: Class zero airways occurred in 0.3% of patients, and the patients with class zero airway had a grade I laryngoscopy. 49.5% of patient had class I, 37.2% class II, 13% of patient had class III and there found no patient with class IV airway. Grade II and III laryngoscopy were more frequent in females than in males but this correlation was not statistically significant. 
Conclusions: Assessment of airway by Mallampati scoring system and attention to the age can be an important factor in the prediction of high laryngoscopy grade.