Concentrations of thirty two polychlorinated biphenyls (PCBs) were determined in the blubber of five sympatric species of odontocetes stranded or by-caught along the Northwest coast of the Iberian Peninsula: common dolphin (Delphinus delphis), long-finned pilot whale (Globicephala melas), harbour porpoise (Phocoena phocoena), striped dolphin (Stenella coeruleoalba) and bottlenose dolphin (Tursiops truncatus). Multivariate analyses were applied to evaluate the ability of PCB patterns to discriminate these sympatric species and to determine which eco-biological factors influence these patterns, thus evaluating the relevance of PCB concentrations as biogeochemical tracers of feeding ecology. The five species could be separated according to their PCB patterns. Different exposure to these contaminants, a consequence of their different dietary preferences or habitats, together with potentially dissimilar metabolic capacities, likely explain these results; sex, age, habitat and the type of prey eaten were the most important eco-biological parameters of those tested. Although, no single congener has been specifically identified as a tracer of feeding ecology, 4 congeners from the 22 analysed seemed to be the most useful and around 12 congeners appear to be enough to achieve good discrimination of the cetaceans studied. Therefore, this study suggests that PCB patterns can be used as tracers for studying the feeding ecology, sources of contamination or even population structure of cetacean species from the Northwest Iberian Peninsula.