Fourty-seven authenticated locality records of the dusky dolphin along the west coast of South America are presented, based on original data, museum specimens and the literature. Confirmed distribution limits are Chimbote (09°05’S) in north—central Peru and Isla Treble (55°07’S 71°02’W), Magallanes, in southern Chile. Accounts are absent from a roughly 1,000 km coastal strip between 36°30’S and 46°S, suggesting the existence of a distribution gap. Specimens encountered south of this area are thought to form part of the Southwest Atlantic population. No abundance estimates are available but fishery mortality data indicate that L.obscurus is the most common cetacean off central Peru and, based on limited sightings, possibly also off northern Chile. Dusky dolphins are present throughout the year off the central Peruvian coast, however consistently larger numbers are caught in winter and spring than in summer. Whether this is due to changes in fishery effort or to seasonal movements of the dolphins, or both, remains unclear. Their habitat in the Southeast Pacific appears to be limited to the coastal branch of the Humboldt Current (i.e. the Fiords Current), with sea surface temperatures mostly ≤ 17°C, although in Peru dusky dolphins have not been observed nearshore. The maximum known offshore range of L.obscurus in the region is approximately 50 nautical miles. Apparently it is absent from Chilean oceanic islands and, generally, from far offshore waters of the Southeast Pacific.