BACKGROUND: Tracheal tube (TT) size selection in children is important to avoid complications. Formulae utilizing age and physical characteristics to predict appropriate tube size are not entirely predictive. METHODS: Using an automated anaesthesia record keeper database, the anaesthetic records of 8504 children, aged up to 7 years, who required tracheal intubation, were reviewed. Age, height and weight data were related to TT size. The total number of patients whose age, height and weight were independently available was 8396, 3929 and 7823, respectively. The number having all three variables was 3814. A linear regression analysis was performed for patients with all three variables and for each variable individually. RESULTS: Tracheal tube size is best predicted using multivariate analysis and, for any child aged up to 7 years, is represented by the formula: 2.44 + (age x 0.1) + (height x 0.02) + (weight x 0.016). Formulae utilizing these variables individually are also reviewed. CONCLUSIONS: Prediction of TT size is best accomplished using multiple variables. Further prospective study is suggested.