We describe the cases of eight patients with chronic idiopathic anhidrosis. These patients were heat intolerant and became hot, flushed, dizzy, dyspneic, and weak but did not sweat when the ambient temperature was high or when they exercised. Four patients had preganglionic sudomotor lesions and in the remaining 4 the lesion appeared to be postganglionic. The patients did not have orthostatic hypotension, other evidence of generalized autonomic failure, or symptomatic somatic neuropathy. One patient regained thermoregulatory sweat function and no patient's condition progressed to generalized autonomic failure. Chronic idiopathic anhidrosis appears to be distinctly different from other autonomic neuropathies that tend to carry much poorer prognoses.