This paper addresses the problem of calibrating a pin-hole camera from images of an isoceles trapezoid. Assuming a unit aspect ratio and zero skew, we introduce a novel and simple camera calibration approach. The key features of the proposed technique are its simplicity and the lack of need for 3D coordinate information about the calibrating object - i.e. the isosceles trapezoid. By ultilizing the symmetry of such trapezoid, we show that one can obtain both the internal and the external camera parameters. To demonstrate the effectiveness of the algorithm, we present the processing results on synthetic and real images, and compare our results to Zhang's flexible calibration method.