Palestinian police have been deployed in Tulkarm after Israel handed over control of the West Bank town.
Tulkarm is one of five cities to be handed over to Palestinian control
The handover - agreed after several days of talks - took place after a dispute over who controlled several nearby villages was resolved.
Tulkarm is the second town in the West Bank after Jericho to come under Palestinian control.
Israel agreed last month to hand security control of five occupied towns back to the Palestinian Authority.
Ramallah, Bethlehem and Qalqilya are also due to be handed over.
Israel promised to hand over the five towns at February's Sharm al-Sheikh summit in Egypt, but this was delayed by a suicide bombing.
The Anabta checkpoint, which controlled the West Bank access to Tulkarm, was reopened for the first time since the Palestinian uprising in 2000.
During the ceremonial handover, the yellow 10m-high gate mounted on concrete blocks was unlocked and an Israeli soldier shouted "Mabruk" - Arabic for congratulations - to his Palestinian counterpart.
Dozens of armed Palestinian police began patrolling the streets of Tulkarm at about 2000 local time (1800 GMT) on Monday.
It was the first time in more than four years that the Palestinians were in control of the northern West Bank town.
Gunmen fired into the air and drivers honked their horns in celebration.
The Tulkarm handover deal was confirmed after a compromise on the security arrangements for the nearby villages.
These included the village from which Palestinian militants mounted February's attack on a Tel Aviv club that killed five Israelis.
Under the deal the villages will remain under Israeli control pending further talks.
On Monday, the Palestinian Authority introduced new weapons restrictions as part of an effort to disarm militant groups.
The new rules limit militants to a single weapon and prohibits them from loading or carrying firearms in public. All weapons must also be registered.
Militant groups said they would not abide by the directive until Israel completed its withdrawal from West Bank towns.