Harbour porpoises are widely distributed in the seas around Denmark. Total abundance in Danish waters is estimated as approximately 100,000 animals. Population density varies considerably by area. There are probably at least two stocks, one in the North Sea and the other in the inner Danish waters and the Baltic, however no definite border line can be drawn. The paper reviews potential threats to harbour porpoise including chemical pollutants, direct exploitation, increased vessel traffic, decreased prey abundance, disease, predation and oil spills. The main threat at present seems to be the levels of bycatch in fishing gear.