"It was very emotional," said Luisa Salaberry, the civil registry worker who officiated at the hospital wedding.
She said that the ceremony was intimate and that the government waived the usual 10 days of bureaucracy because the patient's cancer was so advanced.
"They had been waiting for the law to take effect so that they could get married," said Salaberry, who did not identify the couple.
Civil Registry Director Adolfo Orellano confirmed that the hospital ceremony was Uruguay's first same-sex wedding.
Earlier Monday, TV producer Sergio Miranda and artist Rodrigo Borda, partners for 14 years, were the first to register.
"This is an historic day for us and for the country," Borda said. "No longer will there be first- and second-class citizens. This will be seen in many countries where this option still isn't possible, and hopefully help people in those places live more freely."
Uruguay is the third country in the Americas, after Canada and Argentina, to legalize gay marriage. President Jose Mujica's government also decriminalized abortion and expects senate approval soon for a government-managed marijuana industry.
"This will help so that many people can say, 'I went with my boyfriend to walk in the park,' and not have to invent that they have a girlfriend or something like that," Miranda said.
"There are people who constantly live a double-life," Borda added. "That's why we've made this so visible, to show that it can be done. We're in a country that has a very open mind right now you can see it in the people and in the street."
Borda said U.S. Ambassador to Uruguay Julissa Reynoso is a friend who has been invited to the couple's wedding.
The U.S. Embassy in Buenos Aires on Monday announced an "LGBT Go" campaign, inviting people to apply for up to 60,000 pesos (about $11,000) in grants for projects that protect and strengthen gay rights in Argentina.