There have been isolated reports in the literature of the natural history and less than complete knowledge of the epidemiology and pathophysiology of syringomyelia. This article describes a clinically acute-onset abnormal patient with localized dilatation of the central canal of the spinal cord who had no evidence of present or prior Chiari's malformation, trauma, infection, tumor, or other predisposing pathologic condition. It is suggested that this distinct condition be labeled "acute idiopathic syringomyelia".