Abstract. We show that every tempered distribution, which is a solution of the (homogenous) Klein-Gordon equation, admits a "tame" restriction to the characteristic (hyper)surface {x 0 + x n = 0} in (1 + n)-dimensional Minkowski space and is uniquely determined by this restriction. The restriction belongs to the space S ′ ∂− (R n ) which we have introduced in [16]. Moreover, we show that every element of S ′ ∂− (R n ) appears as the "tame" restriction of a solution of the (homogeneous) Klein-Gordon equation.