William Ian McDonald (15 March 1933 – 13 December 2006) was a New Zealand neurologist and academic.
He was the world leading authority on multiple sclerosis (MS) in the second half of the twentieth century: the McDonald criteria used to diagnose MS are named after him.
McDonald's doctoral thesis dealt with experimental neuropathy in cats induced by diphtheria toxin.
It was conducted at the Department of Physiology under the supervision of Professor Archie McIntyre.
Accolades for his work included 15 prizes for multiple sclerosis research, a dozen honorary fellowships, and honorary membership of 10 overseas neurological associations.