Dr. Tarjan was born in Zsolna, Hungary, received his M.D. (1935) from the University of Budapest in Debrecen, Hungary, and interned at the general hospital in Budapest. He emigrated to the U.S. in 1939 and served another internship at the Memorial Hospital in Kansas City, Missouri (1939–40), followed by a medical residency at the Mercy Hospital in Janesville, Wisconsin (1940–41). He then began a psychiatric residency at the State Hospital in Provo, Utah (1941–43), and in 1943, he entered the Army and served for three years in the Southwest Pacific. He was later discharged as a full Colonel in the Army Reserve.
After leaving the Army, Dr. Tarjan became Director of Clinical Services at Peoria State Hospital, in Illinois. In 1947, he became Superintendent of the Pacific State Hospital, and he later went to the UCLA Neuropsychiatric Institute as Director of the Division of Mental Retardation and Clinical Psychiatry and full professor in the Medical School.
Dr. Tarjan was active in numerous organizations. He served four years on the National Mental Health Advisory Council and was Vice Chairman of the Panel on Mental Retardation. He was President of the Southern California Psychiatric Society (1955–56), A.A.M.D. (1958–59), GAP (1971–76), AACAP (1977–79), a member of the American College of Psychiatrists, and the American Psychopathological Association. He received numerous awards, including the Leadership Award, the AAMS (1970), the Kennedy Foundation (1971), the Award of Merit from the Presidential Commission on Mental Retardation (1972), and the APA Distinguished Service Award (1973).
Dr. Tarjan published six books and over 100 articles, as well as 39 book chapters, mainly in the area of mental retardation.
Dr. Tarjan was Vice President (1967–68), Secretary (1969–72), and served as President of the American Psychiatric Association (1983–84).