A flap valve for a trocar system including a valve housing (12) that is proximally attachable to a guide tube (10), a lead-through opening (30) formed in the valve housing (12), and a pivotally mounted flap valve (46). The flap valve (46) is manually pivotable from a “closed” position to an “open” position via a slide rod. The slide rod (52) is mebedded in the body (12), is radially slidable and contacts with its inner end an actuation area of the flap valve (46).