OBJECTIVE To define the anatomy of the corrugator supercilii muscle (CSM). DESIGN Cadaver dissections following a preset approach. SETTING Anatomy laboratory at a medical school. METHOD Sixteen sides of 8 preserved cadaver heads were dissected. Inferiorly based trapdoor-type flaps were developed in the subgaleal plane. The bone origins of the CSM were first identified. The muscles were then followed to their insertions. The origin and outline of the muscles were plotted on the face of the cadaver. Following the measurements, we transferred the configuration of the CSM to the image of a computer-manipulated face of a model. RESULTS The origin of the CSM has a wide base, spanning across 0.6 cm from the midline and the supraorbital notch/foramen. The area of the muscle origin measured 0.98 x 2.52 cm on the right side and 1.04 x 2.35 cm on the left side. The lateral extent of the CSM insertion measured 4.27 and 4.50 cm from the midline on the right and left sides, respectively. CONCLUSIONS The CSM originates as 3 or 4 thin, rectangular, panellike muscle groups occupying a wide area across 0.6 cm from the midline and the supraorbital notch/foramen. The muscle groups travel parallel to one another in an oblique course without distinguishable oblique or transverse components.