Oxidative reactions are thought to play a role in the inflammatory condition called fatty liver. It is unclear whether oxidized lipoprotein lipids or proteins are associated with future fatty liver. In the Cardiovascular Risk in Young Finns Study, we determined the circulating levels of LDL and HDL oxidized lipids and studied their associations with fatty liver assessed by ultrasonography. There were 1286 middle-aged subjects with normal liver and 288 subjects with fatty liver. Analysis of oxidized lipids consisted of conjugated dienes in isolated HDL (oxHDLlipids) and LDL (oxLDLlipids). Oxidized LDL was also measured with a method based on antibodies against oxidized apolipoprotein B (oxLDLprot). After adjustment for age, sex, leisure-time physical activity, body mass index, alcohol intake, smoking, serum LDL and HDL cholesterol as well as particle concentrations, participants with elevated oxLDLlipids (odds ratio for 1-SD change in oxLDLlipids=1.27, P=0.011) had an increased risk for fatty liver. Similarly, a high oxidation score (oxLDLlipids+oxLDLprot) was directly associated with fatty liver (odds ratio=1.34, P=0.012). The strongest direct association was seen with a high oxLDLlipids/oxHDLlipids ratio (odds ratio=1.49, P=0.001). These data suggest that oxidized lipoprotein lipids are linked with the risk of fatty liver in middle-aged adults. (194/200 words).