1973 was a year in the 20th century.
- Thursday, March 15 (normal timeline): George McFly is honored.
- Thursday, March 15 (Biffhorrific timeline): George is murdered by Biff Tannen.
- Unknown Date (Biffhorrific timeline): Biff Tannen marries Lorraine Baines McFly.
- Unknown Date: Loretta is born to Lewis and Louise.
- Unknown Date: Ito T. Fujitsu known as "The Jits" is born.
Behind the scenes
- Friday, June 15: Neil Patrick Harris (Doogie Howser in The Earth Day Special) is born in Albuquerque, New Mexico.