An FRII radio source with an angular extension of 18.4 arcminutes has been discovered in the Westerbork Northern Sky Survey that is being carried out at 325 MHz. This source is identified with Mrk 1498 at $z=0.056$ indicating that its projected extension is 1.6 \h50\ Mpc. The optical spectrum of Mrk 1498 has the typical emission lines of a narrow line radio galaxy; H$\alpha$ is the only permitted line that has a faint broad component. The discovery shows that the good sensitivity of WENSS at low frequencies to low surface brightness features at scales of a few minutes, is uniquely suited to provide well defined and relatively large samples of giant radio galaxies. The future definition of such samples will be important for our understanding of giant radio galaxies.