On the basis of mineralogical analysis of the tephra layer in the Bioce rock shelter in Montenegro, we revise the cultural and population changes in the eastern Adriatic at the Middle to Upper Paleolithic transition. The disappearance of Neanderthals from that region was traditionally attributed to the Campanian Ignimbrite eruption ~40 ka BP. Comprehensive studies at Bioce by the Russian-Montenegrin expedition in 2010-2015 have resulted in a hypothesis that a Neanderthal refugium existed in the Balkans. We list the lithological and stratigraphic characteristics of the Pleistocene sequence of the site and describe four main strata. Petrographic and x-ray phase analyses and scanning electron microscopy suggest that minerals from samples of ground from horizon 1.3 are of volcanic origin. The comparison of tephra from that horizon with those from local sequences in terms of composition, shape, and size of particles reveals similarity with the Y-5 tephra from the main phase of the Campanian eruption, dating to 39.30-39.85 ka BP. In the habitation sequence of Bioce, the tephra layer is inside lithological stratum 1. Artifacts from that layer and from the overlying and underlying ones, judging by technological and typological criteria, belong to one and the same lithic industry—the micro-Mousterian facies of the local Middle Paleolithic. New findings imply that the Campanian Ignimbrite eruption did not cause the disappearance of the culture associated with Neanderthals in the eastern Adriatic.