Background and objective: The optimal depth of insertion of left-sided double-lumen endobronchial tubes is strongly correlated with body height in average-sized adults. However, this relationship has not been studied in below average-sized adult patients. We investigated whether or not there is a clinically useful relationship in below average-sized adult patients. Methods: One hundred and ninety six consecutive adult patients undergoing thoracic surgery under one-lung anaesthesia (body height ≤ 155 cm) were included in this study. Left-sided double-lumen tubes were inserted under the guidance of a fibre-optic bronchoscope. Optimal depth was defined as the proximal surface of the bronchial cuff positioned just below the carina. Results: There was a statistically significant positive correlation between body height and the optimal depth of insertion (r = 0.61, P < 0.0001); however, the correlation coefficient was low. The actual optimal depth of insertion of one patient was even 4.5 cm shorter than that obtained from the equation. Conclusion: Although there was a statistically significant correlation between body height and the optimal depth of insertion of left sided double lumen tubes in adult patients of short stature (≤ 155 cm), clinical application of the equation is not warranted and these tubes should be inserted under direct vision with a fibre-optic bronchoscope.