The 90th United States Congress began on January 3, 1967. There were four new senators (all Republicans) and 71 new representatives (13 Democrats, 58 Republicans) at the start of the first session. Additionally, five senators (one Democrat, four Republicans) and six representatives (four Democrats, two Republicans) took office on various dates in order to fill vacancies during the 90th Congress before it ended on January 3, 1969.
Due to redistricting in multiple states, eight representatives were elected from newly created seats.