To design a large-volume, low-pressure cuff it is essential to take into consideration cross-sectional shape and circumference of human trachea. Two hundred adult tracheas were dissected and autopsy specimens examined. Cross-sectional tracheal shapes were studied and their circumference measured. There was a definite correlation between sex and the tracheal shapes studied. Forty five per cent of female tracheas were elliptical in shape and 38% were C shaped. The most common cross-sectional tracheal shapes in specimens obtained from male patients were the U shape (33%) and the elliptical (21%). Mean female tracheal circumference was 57.65 mm and mean male tracheal circumference was 68.75 mm. The implications of these findings are discussed and recommendations are made regarding cuff circumference and diameter.