[1] Voting for the Cortes was on the basis of universal suffrage, which comprised all nationals over 18 years of age, registered in Castile and León and in full enjoyment of their political rights.

All members of the Cortes of Castile and León were elected using the D'Hondt method and a closed list proportional representation, with an electoral threshold of three percent of valid votes—which included blank ballots—being applied in each constituency.

Legal amendments introduced in 1998 allowed for these to be held together with European Parliament elections, provided that they were scheduled for within a four month-timespan.

[1][2][4] After legal amendments earlier in 1999, the president was granted the prerogative to dissolve the Cortes of Castile and León and call a snap election, provided that no motion of no confidence was in process, no nationwide election was due and some time requirements were met: namely, that dissolution did not occur either during the first legislative session or within the legislature's last year ahead of its scheduled expiry, nor before one year had elapsed since a previous dissolution.

The highest percentage figure in each polling survey is displayed with its background shaded in the leading party's colour.