After the war he married Ann Margaret Darvall in May 1947. He commenced work as a graduate at the NSW Department of Agriculture, but it became clear to him that he could not get adequate training in Australia. So the couple went to the United States. He studied there for two years, first at the University of Wisconsin–Madison and then at the University of Chicago; five members of that university's economics department present at the time would go on to win the Nobel Prize in Economics. Though he completed the examinations for his PhD, Gruen did not finish the degree as the intensity of his study led to a serious thyroid condition. Without drugs that had been developed shortly before then, the condition would have been life-threatening. However, it was successfully treated and its only legacy for the rest of his life was the exemplary balance Gruen kept in his life. He worked hard and productively, but not obsessively for the rest of his life.