The HSLS was established on 20 May 1989 as the Croatian Social Liberal Alliance and was the first political party established in Croatia still under the communist regime.
HSLS leader Djurdja Adlesic said the party had numerous ups and downs over the past 18 years, going through political puberty and searching its place in Croatian politics.
She said the HSLS had been part of the government twice, walking out both times after assessing that the government's policy clashed with the ideals and principles of the party and liberalism.
Adlesic highlighted 2006 as the year when the HSLS reunited with the Liberal Party (LS) into one party and that about 2,000 new members had joined in the meantime.
She added that this year the HSLS formed a coalition with the Croatian Peasant Party (HSS) to run in elections in the autumn.
Congratulating the HSLS, the president of the ruling Croatian Democratic Union (HDZ), Prime Minister Ivo Sanader, said the HDZ had learned in coalition with the HSLS and other parliamentary parties how a coalition government worked.
Underlining that Croatia needed the liberal idea, he described the HDZ's coalition with the HSLS as a beautiful experience.
Sanader said that although relations in a coalition were not always idyllic, a coalition was a partnership. "Together we raised the threshold of tolerance in Croatia."
Addresses were also made by the HSLS' first president, Slavko Goldstein, and incumbent vice president Zlatko Kramaric, who recalled that the HSLS had been the first political party whose platform was the negation of the then totalitarian policy in all its aspects.
The party was congratulated on its anniversary also by HSS leader Josip Friscic and representatives of other political parties, trade unions and embassies.