The prime minister hosted Mr Juncker at Chequers ahead of a week of efforts to renegotiate Britain’s EU membership.
The EC president “reiterated that he wanted to find a fair deal for the UK”, said a No 10 spokesman after the talks reports BBC.
The meeting came as reports suggest France and Germany are planning to announce further eurozone integration.
French newspaper Le Monde reports that the two countries have agreed a deal to bring about closer political union between eurozone countries without the need for changes to the treaties which govern the EU.
Earlier, No 10 confirmed UK-based citizens from most EU countries would not get a vote. The eligibility rules will be broadly the same as for a general election, rather than for local or European polls.
Mr Cameron has promised to hold an “in-out” referendum by the end of 2017.
The talks between Mr Cameron and Mr Juncker on Monday focused on “reforming the EU and renegotiating the UK’s relationship with it”, the No 10 spokesman said.
“The prime minister underlined that the British people are not happy with the status quo and believe that the EU needs to change in order to better address their concerns.
“Mr Juncker reiterated that he wanted to find a fair deal for the UK and would seek to help.
“They talked through the issue at some length in the spirit of finding solutions to these problems. They agreed that more discussion would be needed, including with other leaders, on the best way forward.”