In 1895, Simpson interned at
Mercy Hospital in
Pittsburgh for a year and became an assistant to Dr. X. O. Werder. He was then assistant gynecologist at Mercy for nine years. In 1903 or 1904, he became chief gynecologist at
Allegheny General Hospital. For a time, he was a consulting gynecologist at Columbia Hospital. In 1916, he became a member of the board of regents of the
American College of Surgeons. In 1919, he was elected secretary general of the International Association of Gynecologists and Obstetricians. In 1915, Simpson was president of the American Gynecological Society. He was an organizer of the American Gynecological Club. He was a member of the Fourteenth International Congress of Physicians and Surgeons. He was secretary general and member of its executive committee of the Seventh International Congress for Obstetrics and Gynecology. He was treasurer of the executive committee of the American Physicians for the Aid of the Belgian Profession. He was a member of the executive committee of the American Society for the Control of Cancer. ==Personal life==