Adopted son of Helen Hayes and Charles MacArthur.
Children (with Joyce Bulifant): Charles, Mary.
Has a daughter, Juliette.
Has a son, with H.B. Duntz, named Jamie MacArthur.
Stated that one of his favorite "Hawaii Five-O" (1968) episodes was "Hawaii Five-O: Retire in Sunny Hawaii... Forever (#8.9)" (1975), because he was able to work on screen with his mother, Helen Hayes (who played his Aunt Clara).
Was the final member of the Hawaii Five-O TV series original cast (1968) to pass away.