The launch of the operation was to be followed tomorrow by a delivery of aid.
"UN teams have pre-positioned food, medical and other basic supplies for immediate delivery as soon as the first group of civilians are out and we hope to send this aid on Saturday morning," said the UN humanitarian coordinator in Syria, Yacoub El Hillo.
"This has been a lengthy negotiation process and we commend all involved for reaching this milestone today," Hillo, who oversaw the launch, said in a statement.
The Homs evacuation is part of a deal brokered by the UN between the two sides after months of negotiations that will also see desperately needed aid delivered.
Red Crescent volunteers aided frail-looking old men wrapped in blankets board a bus, as a woman on a stretcher awaited her turn.
In an amateur video filmed by activists in the nearby Waar area to which they were evacuated, one man smiled as he embraced his son, reunited for the first time in more than 18 months.
Large areas of Syria's third city, dubbed "the capital of the revolution" against President Bashar al-Assad, have been reduced to rubble by fighting between rebels and government forces.
The United Nations said 83 civilians were evacuated under a three-day "humanitarian pause."
"The people who were able to leave were women, children and the elderly," said UN spokesman Farhan Haq.
"They were then delivered to the places of their choice escorted by UN and Syrian Red Crescent staff," he said.
The Syrian Observatory for Human Rights said five of those evacuated were children, while 17 were women.
An AFP correspondent saw some 12 civilians come out on the first bus from the rebel enclave.
Abul Hareth al-Khalidi, a cleric and spokesman for the besieged civilian population, said the evacuation of civilians will continue Sunday.
"On Sunday, we plan for many women and children to leave," he told AFP via the Internet.