William S. Sly (born October 19, 1932) is an internationally known physician and scientist who, except for sabbatical years at Oxford and Stanford, spent his entire academic career in St. Louis.

His group described the first patient with MPS VII (Sly syndrome) and worked with collaborators at The Jackson Laboratory to develop and characterize the mouse model of this disease.

He collaborated with the biotechnology company Ultragenyx to develop enzyme replacement for MPS VII (Sly Syndrome), which went into clinical trials in 2017.

[2] Sly also identified the first inherited deficiency of a human carbonic anhydrase, CA II, and defined the biochemical and molecular genetics of this disorder.

Dr. Sly has also done research on hereditary hemochromatosis, collaborating on studies leading to the cloning of the HFE gene and identification of the product it encodes.