(Roman Koksarov ~ Associated Press)
The parades were supported by the governments of the United States and other Western countries that are pushing for an end to discrimination and violence toward gays.
Homosexuality was a taboo throughout the communist era and that hostility lingers today, despite a growing sense of openness in the region since several of its countries joined the European Union in 2004.
About 2,500 people turned out in Warsaw while some 400 braved rain and hail to march in Riga. The demonstrations are among many gay pride events taking place in June across Europe and elsewhere.
Both the Warsaw and Riga marches required massive police protection. Previous gay pride parades in the Baltics and Poland have been marred by violence and heckling from protesters, though this year the opponents were few and calm.
Ola Osinska, a 28-year-old who held hands with another woman during the Warsaw parade, said she has been attacked in the city three times for being a lesbian.
"It's even worse in small Polish towns," Osinska said. "And even though I have been beaten three times, I am here today because I want to show that I will not hide."
In Riga, U.S. diplomats took part to show their support. They said U.S. Secretary of State Hillary Clinton has asked American officials to be more active in promoting equal rights for lesbian, gay, bisexual and transgender people throughout the world.
"Human rights belong to everyone, regardless of sexual orientation. So we are marching in support of LGBT people here in Latvia, in the Baltics, in Europe, and throughout the world," said U.S. Ambassador to Latvia Judith Garber.
The U.S. Ambassador to Poland, Lee Feinstein, expressed his solidarity for Warsaw's participants though he was out of town. He was among diplomats of about 10 Western countries who signed a letter supporting equal rights for gays and lesbians.
Poland's gays and lesbians have slowly started to become more visible in a society that has long treated homosexuality as a taboo.
A few open-platform trucks pumping techno and pop music and decorated in colorful balloons inched their way down Marszalkowska street, one of Warsaw's key boulevards. Drag queens and other participants danced to the beat.
Two of the trucks belonged to small left-wing parties that support gay rights. The major parties are either hostile or indifferent to the issue.
One of the supportive parties, Palikot's Movement, has made gay rights an issue of public discourse by bringing the country's first openly gay man, and the first transsexual into parliament as lawmakers in elections last year.
The strong influence of the Roman Catholic church has kept many Poles from embracing the gay rights movement.
Agata Trzebuchowska participated in the Warsaw gathering while dressed like St. Mary, her head covered in a blue shroud.
"The situation might be getting better in the political sphere in Poland, but it's not getting better in the church," said the 20-year-old anthropology student.
A group of about 20 people from Belarus also marched in Warsaw as they prepared for a gay pride parade in Minsk in October.
They carried a banner that said, "It's better to be gay than a dictator" -- a quip on a comment Belarus' autocratic President Alexander Lukashenko made earlier this year.
Lukashenko said, "It's better to be a dictator than gay," a statement directed at Germany's gay foreign minister, Guido Westerwelle.
Associated Press writer Gary Peach in Riga contributed to this report.