There 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. The Azov porpoises are distinct in their body size and biology. This 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 significant, whereas in the Sea of Azov the females were significantly larger than males. The Azov skulls were strongly different from those from the Black Sea: they were larger, proportionally wider and had the wider rostra; also, there was no significant chronological variation within the Black Sea. The Azov and Black Sea samples were classified with the 100 % success with four variables. The northwestern Black Sea skulls were somewhat intermediate in their characteristics between the Azov and northeastern Black Sea samples, but they were classify ed together with other Black Sea specimens. The difference between the Azov and Black Sea skulls was greater than between many North Atlantic populations, despite the extreme geographical proximity of the two stocks. The 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. The 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.