1. The frontal sinuses of 250 skulls of Chinese male adults were investigated. Ac-cording to the number of the frontal sinuses, the skulls were classified into five types. Type Ⅰ. no frontal sinus. Type Ⅱ. one frontal sinus (either left or right). Type Ⅲ. two frontal sinuses (one on each side). Type Ⅳ. three frontal sinuses (two left, one right, & vice versa). TyPe Ⅴ. four frontal sinuses (two on each side). 2. The degrees of superior, lateral and posterior extensions of the frontal sinuses inmost cases were grossly symmetrical. 3. It was found that two frontal sinuses were extended posteriorly over the orbitto near the greater and lesser wings of the sphenoid bone. 4. The degree of prominence of the superciliary arches was neither the indicationof the presence of the frontal sinuses nor the estimation of its extension or size. 5. The thickness of the anterior wall of the frontal sinuses was within 0.8--3 mm(89.4% on the left, 84.6% on the right), and the thickness of its septum fluctuated be-tween 0.1--2 mm (70.4%). The septa of all metopic skulls were divided into two partsby the suture. 6. The invading cells and the recesses of the frontal sinuses were studied, classifiedand discussed. 7. The position of the openings of the naso-frontal duct was as follows: 1. drain-age into the ethmoid infundibulum 49.5%. 2. drainage into the frontal recess 26.2%. 3.drainage into the frontal pit 20.5%. 4. drainage into the supra-bulla region 3.8%.