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The physical habitat of cetaceans occurring along the continental slope in the western Ligurian Sea was investigated.Data were collected from two different sighting platforms, one of the two being a whale-watching boat. Surveys, conductedfrom May to October and from 1996 to 2000, covered an area of approximately 3000km2 with a mean effort of about10,000kmyear. A total of 814 sightings was reported, including all the species occurring in the area: Stenellacoeruleoalba, Balaenoptera physalus, Physeter macrocephalus, Globicephala melas, Grampus griseus, Ziphius cavirostris,Tursiops truncatus, Delphinus delphis. A Geographic Information System was used to integrate sighting data to a set ofenvironmental characteristics, which included bottom gradient, area between different isobaths, and length and linearity ofthe isobaths within a cell unit. Habitat use was analysed by means of a multi-dimensional scaling, MDS, analysis.Significant differences were found in the habitat preference of most of the species regularly occurring in the area.Bottlenose dolphin, Risso's dolphin, sperm whale and Cuvier's beaked whale were found strongly associated to welldefineddepth and slope gradient characteristics of the shelf-edge and the upper and lower slope. The hypothesis of habitatsegregation was considered for Risso's dolphin, sperm whale and Cuvier's beaked whale. Canonical discriminant functionsusing depth and slope as predictors outlined clear and not overlapping habitat preferences for Risso's dolphin and Cuvier'sbeaked whale, whereas a partial overlapping of the habitat of the other two species was observed for sperm whale. Such apartitioning of the upper and lower slope area may be the result of the common feeding habits and suggests a possiblecompetition of these three species. A temporal segregation in the use of the slope area was also observed for sperm whalesand Risso's dolphins. Fin whales, and the occasionally encountered common dolphin and long-finned pilot whales showeda generic preference for the pelagic area. In contrast, striped dolphins were generically found in any type of physicalhabitat, in agreement with their known opportunistic feeding habits. Interannual and seasonal movements were observedin fin whales and in all the other regularly occurring species, indicating that changes in the environmental andclimatological conditions have a remarkable influence on habitat use. Finally, a relationship between group size and habitat use was observed for the species known to forage in groups. The relationship suggests that these species respond to environmental variability, either by moving within the study area or by behavioural changes that may reflect changes in the preferences for prey items.