Louis (Lou) Siminovitch (born May 15, 1920) is a Canadian molecular biologist. He was a pioneer in human genetics, researcher into the genetic basis of muscular dystrophy and cystic fibrosis, and helped establish Ontario programs exploring genetic roots of cancer.

Born in Montreal, Quebec to parents who had emigrated from eastern Europe, he won a scholarship in chemistry to McGill University, earning a doctorate in 1944. He then studied at the Pasteur Institute in Paris. In 1953 he joined Toronto's Connaught Medical Research Laboratories. Later he joined the University of Toronto and worked there from 1956 to 1985.

He helped establish the Department of Genetics at the Hospital for Sick Children as geneticist in chief, where he worked from 1970 to 1985. From 1983 to 1994 he was director of research at the Mount Sinai Research Institute.

He is the author or coauthor, at last count, of over 147 scientific papers, reviews, and articles in journals books.

The Elinore & Lou Siminovitch Prize in Theatre is named in his honour.

He married Elinore a writer. They had three daughters. She died in 1995.

Honours

• In 1978 he won the Royal Society of Canada Flavelle Medal
• In 1980 he was made an Officer of the Order of Canada.
• In 1981 he received the Gairdner Foundation Wightman Award.
• In 1988 he was promoted to Companion of the Order of Canada.
• In 1997 he was inducted into the Canadian Medical Hall of Fame.
• In 1999 he was named a foreign associate, and the only Canadian, to the National Academy of Sciences.
• He was awarded a Doctor of Science, Honoris Causa from several Canadian Universities including Memorial University, McMaster University, University of Montreal, McGill University, University of Western Ontario and University of Toronto.