BACKGROUND: We studied the differences in airway assessment factors among old, middle, and young age groups, and evaluated the frequency and causes of difficult intubation among these groups. METHODS: Patients were divided into young (< 40 yr, n = 75 ), middle (40-59 yr, n = 83), and old (> or = 60 yr, n = 89) group. Airway assessment factors such as head and neck movement, thyromental distance, interincisor gap, dentition, Mallampati score, and Arne score were assessed. After muscle relaxation, cervical joint rigidity and Cormack-Lehane (C-L) grade were assessed. The differences in airway assessment factors between difficult (C-L grade 3, 4) and easy (C-L grade 1, 2) intubation were then examined. Logistic regression analysis was also carried out to identify the extent to which airway assessment factors reflected difficult intubation. RESULTS: As aging, head and neck movement, thyromental distance, and interincisor gap decreased, the grade of dentition, Mallampati score, cervical joint rigidity and the ratio of Arne score > 11 increased. In the old and middle group, the incidence of difficult intubation was increased compared with the young group. Dentition in the young group, Mallampati score and interinsisor gap in the middle group and Mallampati score, cervical joint rigidity in the old group respectively predicted difficult intubation. CONCLUSIONS: Compared to young individuals, middle-aged or elderly adults are likely to experience more difficulty in endotracheal intubation and its predictive factors could vary by age group.