We show that, for every x exceeding some explicit bound depending only on k and N , there are at least C(k, N )x/ log 17 x positive and negative coefficients a(n) with n ≤ x in the Fourier expansion of any non-zero cuspidal Hecke eigenform of even integral weight k ≥ 2 and squarefree level N that is a newform, where C(k, N ) depends only on k and N . From this we deduce the existence of a sign change in a short interval.2000 Mathematics subject classification: 11F11, 11F30.