Opitz (born August 15, 1935) is a German-American medical geneticist and professor at the University of Utah School of Medicine.
He is best known for rediscovering the concept of the developmental field in humans (first enunciated by Hans Spemann in amphibians) and for his detection and delineation of many genetic syndromes, several now known as the "Opitz syndromes" including Smith–Lemli–Opitz syndrome (SLOS), Opitz–Kaveggia syndrome (FGS1), Opitz G/BBB syndrome, Bohring–Opitz syndrome, and other autosomal and X-linked conditions.
He is founder of the Wisconsin Clinical Genetics Center, the American Journal of Medical Genetics, and the American College and American Board of Medical Genetics.