The paper proposes a new calibration algorithm for cameras with lens distortion, that uses a single image of a planar chessboard pattern acquired in general position. The radial distortion is modeled using the first order division model, and the method provides a closed form estimation of the intrinsic parameters and distortion coefficient. The experimental evaluation shows that the calibration accuracy is comparable to state-of-the-art algorithms requiring multiple input images. We believe that our approach is particularly well suited for the the calibration of medical endoscopes in computer aided surgery. Since the lens is mounted on the camera before each usage in the OR, the calibration procedure must be performed by the clinical practitioner with minimum effort. We solve this problem by proposing a fully automatic procedure that requires no human intervention other than acquiring a single calibration image.