A survey of harbour porpoises (Phocoena phocoena) was carried out at five sites (North County Dublin, Dublin bay, Cork coast, Roaringwater bay cSAC and Galway bay) to derive density and abundance estimates. Single platform line-transect surveys were carried out on six days at each site between July and September 2008. Distance sampling was used to derive g(0), which is the density of harbour porpoises on the track of the vessel. Abundance estimates were calculated using the track-line as the sample and the sighting as the observation. During 28 survey days a total of 354 track-lines were surveyed for a total distance of nearly 20,000 km in seastate ≤2. From the 269 sightings of a total of 496 individual harbour porpoise were recorded. There were 13 sightings with a total of 171 common dolphins (Delphinus delphis), eight sightings of single minke whales (Balaenoptera acutoratrata) and one sighting of 20 bottlenose dolphins (Tursiops truncatus). Five sightings with a total of 18 dolphins were not identified to species level.