Swayback (enzootic ataxia), a disease not previously described in Canada, occurred in newborn lambs in Alberta in 1972. Of 100 lambs born in one flock, over 60 succumbed in the enzootic. The diagnosis was based on the presence of a) gross cavitations and gelatinous lesions of the cerebral white matter in 16 of 24 (66.67%) lambs examined, b) central chromatolysis and hyalinization of neurons of the red and vestibular nuclei and reticular formation and of the lateral and ventral horns of the spinal cord, c) myelin deficiencies of the dorsolateral and sulcomarginal funiculi of the spinal cord and d) low hepatic and serum copper levels in affected lambs and low serum copper levels in the ewes. The feeding of sugar beet-(beta saccharifera) top silage to the ewes during pregnancy, lambing and lactation, and its relationship to the enzootic is discussed.