We report two women who presented with a Guillain-Barré syndrome just after a ketoacidosic comatose state disclosing an insulin-dependent diabetes mellitus. One had characteristic clinical signs and the other had major motor involvement. At neurophysiologic investigations, one had typical demyelinating neuropathy whereas the second had mainly axonal degeneration. At ultrastructural examination of a peripheral nerve biopsy, features of macrophage-associated demyelination were present in both nerve specimens, thus confirming the diagnosis of acute inflammatory demyelinating polyneuropathy, i.e., Guillain-Barré syndrome. Prominent axonal involvement was also present in the motor nerves of the second patient. Insulin therapy had to be permanently continued and these two cases are quite different from the transient diabetes sometimes observed in certain cases of Guillain-Barré syndrome. Both the latter and insulin-dependent diabetes mellitus probably have auto-immune mechanisms. It is likely that in our two patients both auto-immune diseases were triggered by a common event. Such cases of Guillain-Barré syndrome have to be distinguished from other acute diabetic neuropathies.