Documented sightings of harbour porpoises in the Mediterranean are rare, although the species is common in the neighbouring North Atlantic and Black Sea. However, in the past 2 decades, 4 harbour porpoises Phocoena phocoena have been recorded in the northern Aegean Sea in the eastern Mediterranean Basin. Samples were taken from 2 of these. Both have a genetic signature indicative of the Black Sea and their age and small size further suggest they originated from the Black Sea rather than the Atlantic population. These results are the first to indicate probable movement of porpoises out of the Black Sea and into the Mediterranean Sea.