This annual report presents the results of post-mortem examinations of stranded harbour porpoises in 2020. One of the main objectives of the research is to quantify human-induced causes of death. In 2020, 49 dead harbour porpoises were examined: 27 males and 22 females, 28 adults, 9 juveniles and 12 neonates. In addition 3 foetuses were found. Most of the examined harbour porpoises died as a result of infectious diseases (37%) and grey seal attacks (20.4%). Trauma of other origin was the most likely cause of death for 6 porpoises (12.2%) and bycatch for one porpoise (2%).