The reported decline of the harbour porpoise in the coastal areas of the North Sea after 1940, has also been seen in Dutch waters. Information on the distribution and abundance of harbour porpoises in this area was scarce until 1972, when systematic counts of seabirds from coastal sites in the Netherlands started and sightings data on harbour porpoises were also collected. Ship-based counts of seabirds commenced in 1987, during which opportunistic observations of cetaceans were made. Effort was concentrated in the Dutch sector of the North Sea. During the winter harbour porpoises were most abundant in Dutch, German and Danish coastal waters off the Wadden Sea, and density was low further offshore. This changed gradually towards the summer, when few harbour porpoises were seen within 40km off the coast. The latter observation has been corroborated by the results from the 1994 SCANS summer survey. The reverse was noted during the autumn. The species appears to have made a slight recovery, at least in the winter, after a serious decline from 1940-1960. Highest numbers were recorded in winter 1993/1994. This paper further elaborates on the state of knowledge and the type of related research carried out in the Netherlands on bycatch – the largest threat to harbour porpoises in the North Sea – and on pollution and epizootic-related virology.