The role of the crevice-opening dimension, a, on the stability of crevice corrosion was investigated in the Ni/1 N H2SO4 system. The electrode potential and current distributions inside the crevice were measured and calculated, respectively. Other variables, in particular the composition of the electrolyte, were constrained from changing during the experiment The passive/active boundary, x(pass), moved further into the crevice for increasing a, and was in close agreement with the calculated value using the IR = Delta Phi* relation. A sharp upper limiting value, a(lim) or a given crevice depth, l, above which crevice corrosion does not occur, was predicted and experimentally observed. The potential E-pass at x(pass) on the crevice wall. corresponded approximately to the potential of the passive/active transition df the bulk solution polarization curve.