1991 Mexican legislative election

Legislative elections were held in Mexico on 18 August 1991, alongside gubernatorial elections in six states. The Institutional Revolutionary Party (PRI) won 320 of the 500 seats in the Chamber of Deputies and 31 of the 32 seats up for election in the Senate. Voter turnout was 61% in the Chamber election and 62% in the Senate election.

Background
Prior to the legislative elections, a historic milestone occurred in 1989 when Ernesto Ruffo Appel of the National Action Party (PAN) was elected governor of Baja California in state elections, becoming the first governor not from the PRI in sixty years. This started a succession of state election victories for the PAN and the Party of the Democratic Revolution (PRD).

The Federal Electoral Institute (IFE), an independent public organization tasked with organizing elections for the presidency and Congress, officially came into being on 11 October 1990.

Electoral system
Of the 500 members of the Chamber of Deputies, 300 were elected in single-member districts by first-past-the-post voting, while 200 were elected by proportional representation. In order to assure absolute legitimacy and reliability for the 1991 elections, an entirely new electoral roll was created without reference to previous rolls. In 1991 there were an estimated 45 million citizens over the age of 18, and an electoral roll of over 39 million people was created in eight months.

Half of the 64 Senate seats were up for election.

Campaign
The election campaign was largely focussed on economic issues, and the elections were characterised by some political commentators as a referendum on the economic reforms of President Carlos Salinas de Gortari.