The new Electroslag Remelting plant established in FOMAS Osnago (Italy) few years ago regularly produces ingots up to 2000 mm diameter and 125 tons. In order to understand the behaviour of the ESR process in the final part of the remelting, some tests were run on hot topping of 2000 mm diameter mould to evaluate the depth of the liquid pool and morphology and distribution of possible internal defects. Detailed ultrasonic inspection was carried out on the forged ingot in order to map the dimensions and position of the indications. In order to give a reliable evaluation of the nature of the detected discontinuities, a further plastic reduction was applied to check if the indications disappeared (empty porosities) or moved and reduced in dimensions (slag entrapments). We calculated by a finite elements dedicated software the new theotetical position and morphology of initial defects after the application of the plastic flow, simulating both voids and inclusions. The results of FEM simulation perfectly overlap final ultrasonic evidences and results of destructive tsts based on optical and electronic microscopy. These results make it possible to know the "worst case" fot the depth of internal defects below the head of remelted ingots and subsequently to oprimize the use of remelted ingots and the calculation of total ingot weight needed for forgings with different geometry.