Levels of omega-3 (n-3) and omega-6 (n-6) fatty acids and lipid-adjusted concentrations of polychlorinated biphenyls (PCBs), dioxins, toxaphene, and dieldrin were determined in 459 farmed Atlantic salmon, 135 wild Pacific salmon, and 144 supermarket farmed Atlantic salmon fillets purchased in 16 cities in North America and Europe. These were the same fish previously used for measurement of organohalogen contaminants. Farmed salmon had greater levels of total lipid (average 16.6%) than wild salmon (average 6.4%). The n-3 to n-6 ratio was about 10 in wild salmon and 3-4 in farmed salmon. The supermarket samples were similar to the farmed salmon from the same region. Lipid-adjusted contaminant levels were significantly higher in farmed Atlantic salmon than those in wild Pacific salmon (F = 7.27, P = 0.0089 for toxaphene; F = 15.39, P = 0.0002 for dioxin; F > or = 21.31, P < 0.0001 for dieldrin and PCBs, with df = (1.64) for all). Levels of total lipid were in the range of 30-40% in the fish oil/fish meal that is fed to farmed salmon. Salmon, especially farmed salmon, are a good source of healthy n-3 fatty acids, but they also contain high concentrations of organochlorine compounds such as PCBs, dioxins, and chlorinated pesticides. The presence of these contaminants may reduce the net health benefits derived from the consumption of farmed salmon, despite the presence of the high level of n-3 fatty acids in these fish.