The Royal College of General Practitioners (RCGP) said the figure had fallen to 351 from 366 in 2004/05.
In the same period, the number of registered patients rose by more than 125,000 to 1.92 million - an average increase per surgery of more than 500.
The RCGP said Northern Ireland had the lowest number of GPs per patient in the UK; a shortfall equating to 234 GPs.
RCGP chairman Dr John O'Kelly said: "With growing numbers of patients, and fewer GP surgeries, general practice is creaking at the seams.
"But this pressure and the danger it poses to our patients has not yet been adequately recognised by decision makers.
"Whilst other countries in the UK are being promised increased resources to cope with increasing patient demand, in NI - where our patients already have fewer GPs per head - general practice has largely been ignored."
Northern Ireland has been allocated about Â£41m in additional public spending next year.
This is Stormont's share of the extra Â£2bn allocated to the UK health service by Chancellor George Osborne in his Autumn Statement.
However, the Northern Ireland Executive is not obliged to spend the extra money on health.
Dr O'Kelly said the money should be used to invest in stronger local GP services.
"To gain parity with other UK nations, we urgently need a package of measures to encourage more young doctors to enter the GP workforce, retain and support current GPs, and make it easier for those who have left the workforce to come back," he said.
The number of GP surgeries in Northern Ireland at its lowest since 1991, a group of doctors has said.