Abstract. Let g be a Lorentzian metric on the plane R 2 that agrees with the standard metric g 0 = −dx 2 + dy 2 outside a compact set and so that there are no conjugate points along any time-like geodesic of (R 2 , g). Then (R 2 , g) and (R 2 , g 0 ) are isometric. Further, if (M, g) and (M * , g * ) are two dimensional compact time oriented Lorentzian manifolds with space-like boundaries and so that all time-like geodesics of (M, g) maximize the distances between their points and (M, g) and (M * , g * ) are "boundary isometric", then there is a conformal diffeomorphism between (M, g) and (M * , g * ) and they have the same areas. Similar results hold in higher dimensions under an extra assumption on the volumes of the manifolds.