Background and objective: Preoperative evaluation is important in the detection of patients at risk for difficult airway management. It is still unclear whether true prediction is possible and which variables should be chosen for evaluation. The aim of this prospective, multi-centre study was to investigate the incidence of difficult intubation, the sensitivity and positive predictive values of clinical screening tests and whether combining two or more of these tests will improve the prediction of difficult intubation in Turkish patients. Methods: Seven study sites from six regions in Turkey participated in this study. One thousand six hundred and seventy-four ASA physical status I-III patients, scheduled to undergo elective surgery under general anaesthesia, were included. Results: The incidence of difficult intubation was 4.8% and increased with age (P < 0.05). The incidence of difficult intubation was significantly higher in patients who had a Mallampati III or IV score, a decreased average thyromental and sternomental distance, decreased mouth opening, or decreased protrusion of the mandible (P < 0.05). Mouth opening and Mallampati III-IV were found to be the most sensitive criteria when used alone (43% and 35%, respectively). Combination of tests did not improve these results. Conclusions: There is still no individual test or a combination of tests that predict difficult intubations accurately. Tests with higher specificity despite low positive predictive value are needed.