Gajdusek was born in Yonkers, New York, on September 9, 1923, the son of Hungarian immigrants. His parents provided a rich intellectual environment at home, and Gajdusek became interested in science at an early age. While still in high school, he spent summers working at the Boyce Thompson Institute for Plant Research in Yonkers. Gajdusek entered the University of Rochester in 1940 at the age of 16. He graduated with a bachelor of science degree in biophysics three years later. In 1946, he also received an M.D. from Harvard Medical School.

In the eight years following graduation from Harvard, Gajdusek completed residencies in Boston, Massachusetts, and New York City, New York, worked for two years at the California Institute of Technology with Linus Pauling, did research in virology at Harvard with John Enders, served in the United States Army at the Walter Reed Medical Center, and continued his studies in Iran at...