A prospective study in South-East England during 15 months in 1983-1984 recruited 100 patients with acute idiopathic neuropathy. After 12 months 67% had recovered completely, 20% were still significantly disabled and 13% had died. Ten of the 13 deaths were attributable to the neuropathy. The major features in the initial assessment which were associated with persistent disability were the time taken to become bedbound, requirement for ventilation, age greater than 40 years, and small or absent compound abductor pollicis brevis muscle action potentials elicited by stimulation of the median nerve at the wrist. These four variables have been combined in a statistical model to predict outcome for individual patients with acute idiopathic neuropathy.