In 1965 Stouthuysen was officially appointed director of the company. In 1971 he was appointed as a member of the board of directors and in 1987 he became the director and in 1988 president of Janssen Operations Worldwide.
In 1965 Stouthuysen was formally designated as the head of the company. In 1971 he was appointed to serve on the board of directors, and in 1987 he took on the role of director, eventually becoming president of Janssen Operations Worldwide in 1988.