OBJECTIVE:This prospective, observational study aimed to identify children likely to require sedation preoperatively by measuring anxiety levels using the modified Yale Preoperative Anxiety Scale (mYPAS). Other possible predictive factors for preoperative sedation were also investigated. METHODS: A total of 455 patients aged 2 -12 years scheduled for surgery requiring general anaesthesia were enrolled in the study. Patients' anxiety levels were measured using the mYPAS in a preoperative holding area just before patients were separated from their parents or guardians and entered the operating theatre. Anaesthetists blinded to the mYPAS assessments judged whether the child could be separated and enter the operating theatre without a sedative. The ability of the mYPAS to predict the need for preoperative sedation was analysed by receiver operating characteristic (ROC) curve analysis. RESULTS: The optimum mYPAS cut-off for requiring sedatives was 41.7 according to ROC curve analysis. Multivariate logistic regression analysis showed that age, mYPAS > 40 and waiting time were independent predictors of the requirement for sedative administration. CONCLUSIONS: High anxiety levels, young age and long waits contributed to the need for preoperative sedation in children.