The Regional Assembly of Cantabria was the devolved, unicameral legislature of the autonomous community of Cantabria, having legislative power in regional matters as defined by the Spanish Constitution and the Cantabrian Statute of Autonomy, as well as the ability to vote confidence in or withdraw it from a President of the Regional Deputation. Voting for the Parliament was on the basis of universal suffrage, which comprised all nationals over eighteen, registered in Cantabria and in full enjoyment of their political rights. The 39 members of the Regional Assembly of Cantabria were elected using the D'Hondt method and a closed list proportional representation, with a threshold of 5 percent of valid votes—which included blank ballots—being applied regionally. Parties not reaching the threshold were not taken into consideration for seat distribution. The electoral law provided that parties, federations, coalitions and groupings of electors were allowed to present lists of candidates. However, groupings of electors were required to secure the signature of at least 1 percent of the electors registered in Cantabria. Electors were barred from signing for more than one list of candidates. Concurrently, parties and federations intending to enter in coalition to take part jointly at an election were required to inform the relevant Electoral Commission within ten days of the election being called.
Election date
The term of the Regional Assembly of Cantabria expired four years after the date of its previous election. Election day was to take place between the thirtieth and the sixtieth day from the date of expiry of parliament. The previous election was held on 8 May 1983, which meant that the legislature's term would have expired on 8 May 1987. The election was required to take place no later than the sixtieth day from the date of expiry of parliament, setting the latest possible election date for the Parliament on Sunday, 7 July 1987. The Regional Assembly of Cantabria could not be dissolved before the date of expiry of parliament except in the event of an investiture process failing to elect a regional President within a two-month period from the first ballot. In such a case, the Regional Assembly was to be automatically dissolved and a snap election called, with elected deputies merely serving out what remained of their four-year terms.
Opinion polls
The table below lists voting intention estimates in reverse chronological order, showing the most recent first and using the dates when the survey fieldwork was done, as opposed to the date of publication. Where the fieldwork dates are unknown, the date of publication is given instead. The highest percentage figure in each polling survey is displayed with its background shaded in the leading party's colour. If a tie ensues, this is applied to the figures with the highest percentages. The "Lead" column on the right shows the percentage-point difference between the parties with the highest percentages in a given poll. When available, seat projections are also displayed below the voting estimates in a smaller font. 20 seats were required for an absolute majority in the Regional Assembly of Cantabria.
