Acute dysautonomia is a disorder characterized by severe sympathetic and parasympathetic failure with relative preservation of motor and sensory function. The disease is considered to be idiopathic in most cases, but there is now a trend towards considering the disorder as an uncommon variant of Guillain Barré syndrome. We report two cases of acute dysautonomia which did not fulfill the criteria of the idiopathic form. The first case was associated with Sjögren's syndrome and the second with thyroiditis and antiganglioside antibodies which were correlated with the severity of the disease. Intravenous gammaglobulin (IVGG) was effective in both cases, as has been reported for the idiopathic form, and in one case the treatment was associated with an increase in the supine and standing plasma norepinephrine levels, thus substantiating the positive effects of IVGG on the orthostatic blood pressure and heart rate. We conclude that the spectrum of acute dysautonomia is superimposable on that of the inflammatory peripheric neuropathies and should include both the idiopathic form and dysautonomia with autoimmune associated disorders. IVGG are effective and seems to act by increasing plasma norepinephrine levels.