When Leila D. Denmark, left her office for the last time in the spring of 2001, her retirement from the practice of pediatrics marked the end of more than seven decades as a practicing physician. At the age of 103 years, she was thought to be the oldest living medical doctor in the United States at the time of her retirement, a person who had seen medicine from the days before immunizations to the advanced medical technology of the 21^st century.