The first electoral test for José Luis Rodríguez Zapatero as leader of his party took place one year before being appointed prime minister of Spain.

The 2004 General Election was preceded by the Local and Regional Elections of May 25, 2003. The Socialist Party received a larger popular vote (what prompted Zapatero to claim his party had been the winner) but the People's Party obtained more government posts in councils and regional governments. In general, there were not too many changes in the results compared to those of the previous Elections held in 1999.

Some interesting data was extracted from the outcome of the election. For example, the results in the areas affected by the Prestige disaster were especially good for the People's Party. Zapatero's opponents claimed that they proved that the Government handling of the crisis had been adequate and that Zapatero's criticisms had been unfair, demagogical and electioneering.

Another interesting fact was the defeat of the People's Party in the Autonomous Community of Madrid. After the election, the People's Party lacked two seats in the Regional Assembly to obtain an absolute majority. This allowed an alliance of Socialists and Communists to grab the power. The situation was amply welcome by Zapatero for propagandistic reasons: until then whoever had won in Madrid had also won the next General Election. But an unexpected event happened. Two socialists MPs angry at the distribution of power in the future regional government between the Communist Party (called in Spain Izquierda Unida, United Left) and the Socialist Party started a crisis that led to the repetition of the Election in Madrid in October 2003 with the subsequent victory of the People's Party. This event has been one of the most obscure in Spanish recent democratic history. Zapatero did not accept the version of the socialist MPs and tried to explain it through a conspiratorial plot caused by speculative interests of the house building industry that would have bribed the MPs to prevent a Left-wing government. The People's Party, on the other hand, defended the theory that the anger of the two Socialist MPs was caused by a failed Zapatero's promise about the referred distribution of power within the Madrid section of the Socialist Party. That promise would have been made some months before the crisis in exchange of support for one of his more immediate collaborators (Trinidad Jiménez ), who wanted to become the Socialist candidate to Mayor of Madrid (the Spanish capital).