Two Tanzanian patients with konzo were severely disabled by a non-progressive spastic paraparesis, since the sudden onset during an epidemic six years earlier. At the time of onset they had a high dietary intake of cyanide from exclusive consumption of insufficiently processed bitter cassava roots. MRI of brain and spinal cord were normal but motor evoked potentials on magnetic brain stimulation were absent, even in the only slightly affected upper limbs. Other neurophysiological investigations were largely normal but the more affected patient had central visual field defects. Konzo is a distinct disease entity with selective type upper motor neuron damage.