Th ere are two porpoise stocks in the northern Black Sea: the north-western (Odessa Gulf) and northeastern (Crimean and Caucasian waters); in addition, another stock is in the Sea of Azov. Th e Azov porpoises are distinct in their body size and biology. Th is research was conducted on the skulls of stranded sexually mature porpoises from the north-eastern Black Sea, north-western Black Sea and the Sea of Azov. In the north-eastern Black Sea samples, both present-day and old-time, the sexual dimorphism of the skull size was not signifi cant, whereas in the Sea of Azov the females were signifi cantly larger than males. Th e Azov skulls were strongly diff erent from those from the Black Sea: they were larger, proportionally wider and had the wider rostra; also, there was no signifi cant chronological variation within the Black Sea. Th e Azov and Black Sea samples were classifi ed with the 100 % success with four variables. Th e northwestern Black Sea skulls were somewhat intermediate in their characteristics between the Azov and northeastern Black Sea samples, but they were classifi ed together with other Black Sea specimens. Th e diff erence between the Azov and Black Sea skulls was greater than between many North Atlantic populations, despite the extreme geographical proximity of the two stocks. Th e low variation within the Black Sea supports the earlier conclusions on the lack of genetic variation: all the Black Sea stocks are expected to be genetically similar sub-populations, whereas the Azov and Marmara stocks possibly represent the genetically distant populations. Th e porpoises from the Black Sea and the Sea of Azov equally show the traits which characterize the subspecies Phocoena phocoena relicta, but the Black Sea porpoises appear to be more paedomorphic in terms of ontogenetic trajectories.