Cohen joined the Yale School of Medicine in 1972.[2] Along with other researchers, he had begun looking at non-psychological (organic) causes for Tourette syndrome (TS) by 1976.[7] Cohen was named the director of the Yale Child Study Center in 1983—a position he held until his death in 2001.[2] In 2000, he was named the Sterling Professor of Child Psychiatry, Pediatrics and Psychology at Yale.[2] At Yale, he studied personality development, TS treatment, the effects of stress on developing children, and the interplay between genetic and environmental factors in neuropsychiatric disorders.[1]