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Purpose: To describe the correlation between clinically measured hyomental distance ratio (HMDR_clin) and the ultrasound measurement (HMDR_echo) in patients with and without morbid obesity and to compare their diagnostic accuracy for difficult airway prediction. Methods: HMDR_clin and HMDR_echo were recorded the day before surgery in 160 consecutive consenting patients. Laryngoscopy was performed by a skilled anesthesiologist, with grades III and IV Cormack&#8722;Lehane being considered difficult views of the glottis. Linear regression was used to assess the correlation between HMDR_clin and HDMR_echo and receiver operating curve analysis was used to compare the performance of the two for predicting difficult airway. Results: The linear correlation between HMDR_clin and HDMR_echo in patients without morbid obesity had a Pearson coefficient of 0.494, while for patients with morbid obesity this was 0.14. A slightly higher area under the curve for HMDR_echo was oberved: 0.64 (5%CI 0.56&#8722;0.71) versus 0.52 (95%CI, 0.44&#8722;0.60) (<i>p</i> = 0.34). Conclusion: The association between HMDR_clin and HDMR_echo is moderate in patients without morbid obesity, but negligible in morbidly obese patients. These might be explained by difficulties in palpating anatomical structures of the airway.