Nils Berglund and Barbara Gentz Universality of residence-time distributions\\ in non-adiabatic stochastic resonance (262K, Postscript) ABSTRACT. We present a mathematically rigorous expression for the residence-time distribution of a periodically forced Brownian particle in a bistable potential. For a broad range of forcing frequencies and amplitudes, the distribution is close to a periodically modulated exponential one. Remarkably, the periodic modulation is governed by a universal function, depending on a single parameter related to the forcing period. The behaviour of the distribution and its moments is analysed, in particular in the low- and high-frequency limits.