At least 16 people have drowned in the narrow strait separating Turkey from the Greek island of Lesbos, say authorities and the UN.
Two children were among those whose bodies were recovered.
There were two survivors, including a pregnant woman. The survivors, from Cameroon and the Democratic Republic of Congo, said there had been between 20 and 25 people on board.
Hundreds of people have died since 2015 trying to cross from Turkey to Greece.
The numbers dropped dramatically from March last year, after Turkey and the EU agreed a deal to stem the flow of people.
But there are fears that numbers attempting the crossing could begin to rise again if the deal is affected by nose-diving relations between the two sides.
The bodies of six women, a child and two men were recovered in Greek territory, while six men and a child were found in Turkish waters, said Greek and Turkish coastguard officials.
The survivors said the boat had capsized on Sunday night.
"The number of people crossing the Aegean to Greece has dropped drastically over the past year, but this tragic incident shows that the dangers and the risk of losing one's life remains very real," said Philippe Leclerc, Greece representative for the UN's refugee agency UNHCR, according to Reuters news agency.
In a separate incident, an Iranian man died amid a high-speed chase involving a van of illegal migrants and Greek police near Greece's north-eastern border with Turkey after the van overturned, reported AFP news agency.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries such as Syria, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.