Very little is known about tissue changes and pathophysiological mechanisms in Garin-Boujadoux-Bannwarth syndrome. We report histopathological findings in the central and peripheral nervous systems of three typical cases. In the acute stage of the disease mononuclear perivascular infiltrations with mainly T-helper cells were the prominent finding, whereas after treatment there was no vessel involvement. The fibre changes in the peripheral nervous system consisted of axonal degeneration. No Borrelia burgdorferi-specific antigen could be detected by immunohistochemical methods. Thus vasculitis might be one of the primary pathophysiological mechanisms for the involvement of the nervous system.