Slow saccadic eye movements occur in some patients with Huntington's disease (HD), and minor defects of supranuclear eye movement control can be demonstrated in the majority by neuroophthalmological laboratory methods. In the pathogenesis of slowed saccades, a lesion of the paramedian pontine reticular formation and specifically the nucleus pontis centralis caudalis was considered likely due to similar eye movement disturbances in well documented degenerative and vascular lesions of the lower pontine tegmentum. A systematic morphometric study was performed on the nucleus pontis centralis caudalis in 9 patients with HD. Two of them had grossly defective saccades during life, and 7 had normal eye movements on routine examination. In 8 patients, the nucleus was reduced in size, revealed a higher than normal neuronal density, and a striking loss of large neurons. One patient with HD and normal morphometric results had died 2 years after the onset of chorea from an unrelated illness. It is proposed that the nucleus pontis centralis caudalis is regularly affected in HD and that progressive loss of large neurons is the cause of saccadic slowing.