1978 Spanish constitutional referendum

The new constitution was intended to replace the many constitutional laws of the Franco era, the Fundamental Laws of the Realm, and turn Spain into a constitutional monarchy by removing many of the King's powers. The feat of creating a democratic system without breaking the structures of power of the state was made possible by the approval of the Political Reform Act of 1977, passed by the Francoist Cortes as the last Fundamental Law. It had been drafted by the President of the Cortes Españolas, Torcuato Fernández-Miranda (including changes that would replace the Cortes Españolas with a Cortes Generales), and supported by Prime Minister Adolfo Suárez and King Juan Carlos. The law provided for the legalization of political parties and a democratic election to Constituent Cortes, a committee of which then drafted the Constitution.[4]

Some Spanish media found up to 30% of irregularities in the census in certain provinces, with many people allegedly being unable to vote while others voted twice.[6] Adolfo Suárez's government had lowered voting age from 21 to 18 only three weeks before the referendum, which resulted in a made-up electoral register increasing by over 3 million people compared to the 1977 general election amid technical, administrative and logistical issues.[7] Interior Ministry officials acknowledged deviations of up to 5.1 per 100 in the electoral census—roughly 1.5 million people according to the National Institute of Statistics—resulting from the absence of an official electoral register and in an overreliance on data from municipal registers.[8]