Biostratigraphic study of Late Miocene (Pannonian and Pontian) endemic molluscs from east Hungarian part of the Pannonian Basin revealed the relative persistence of the deep water association (Paradacna abichi, Dreissenomya digitifera, „Pontalmyra” otiophora, Valenciennius etc.) during the Late Pannonian and Pontian. Consequently, the earlier inpretation of these forms as Pontian or Lower Pontian ones, and definition of the Early and Late Pontian substages by them, should be revised. The occurrences of the sublittoral association can be divided into two stratigraphic units: Congeria czjzeki and Lymnocardium aff. winkleri indicate Late Pannonian, while their descendants, i.e. C. zagrabiensis and L. majeri, indicate Pontian age. In the littoral facies zone 3 stratigraphic units were identified: a Late Pannonian one, an Early Pontian one (with Lymnocardium decorum), and a Late Pontian one (with Prosodacnomya). Evolution from L. decorum to Prosodacnomya took place between 7.7 and 7.0 million years, according to magnetostratigraphic and seismic data. Basinward progradation is demonstrated by the geographic distribution of molluscs. The Pannonian-Pontian boundary, just like the other isochronous surfaces, has a dip towards the interior of the basin. It runs in the delta plain facies in the northern part of˙the˙Tiszantul area, further to the south it intersects the slope facies, and reaches the basement at the feet of the southeastern Hungarian pre-Neogene highs. Consequently, in the northern part of Eastern Hungary Pannonian, and in the southern part Pontian sediments give the major part of the basin fill.