PURPOSE: To evaluate the radiologic characteristic of acute inflammation of the epiglottis and supraglottic structures in adults. METHODS: The clinical and radiographic findings in 27 adult patients with epiglottitis (average age, 43 years; range, 28 to 81 years) were compared with those of a control group of asymptomatic subjects (n = 15; average age, 48 years; range, 24 to 79 years). Unusual clinical aspects in the current series included two patients who were positive for human immunodeficiency virus, 1 with acquired immunodeficiency syndrome and Kaposi sarcoma, 3 with emphysematous epiglottitis, 1 with abscess formation, and 1 with laryngeal carcinoma. One patient required emergency tracheostomy. One patient died of pneumonia. RESULTS: The ratio of the soft-tissue parameters to the anteroposterior width of the C-4 vertebral body yielded three key parameters of high statistical significance in adult epiglottitis. The ratio of the width of the epiglottis to the anteroposterior width of C-4 should not be greater than 0.33 (sensitivity, 96%; specificity, 100%). The ratio of the prevertebral soft tissue to C-4 should not exceed 0.5 (sensitivity, 37%; specificity, 100%) and the ratio of the width of the hypopharyngeal airway to the width of C-4 should be less than 1.5 (sensitivity, 44%; specificity, 87%). The aryepiglottic folds were enlarged in 85%, and the arytenoids were swollen in 70% of the patient population (specificity, 100%). CONCLUSION: These defined radiologic parameters should aid in the diagnosis of acute epiglottitis in adults.