A mosasaurid skull, 6 cervicals, the anterior two dorsals and a single posterior dorsal vertebra were found in Oron, Negev Desert, Israel, in latest Campanian deposits. The skull is dorsoventrally compressed and somewhat distorted, but otherwise in good condition, although sutures are often indistinct, in part due to weathering and in part due to the great size and presumable old age of the specimen. At an overall length of 1,422 mm it is one of the largest skulls ever discovered. The skull bears resemblance to those of advanced mosasaurines, in particular the type species of Prognathodon, P. solvayi, but differs from all previously known mosasaurids in having a frontal distinctly wider than long. Cladistic analysis on cranial and mandibular characters of 33 ingroup taxa were performed. A Nelsen consensus tree (1:225, ci:44 ri:76) based on 3 equally parsimonious trees placed this new specimen as the sister taxon to P. solvayi, with the American species of Prognathodon forming successive outgroups to these two. The present specimen extends the size range of known globidensine mosasaurines by around a factor two.