The composition of fatty acids in serum cholesteryl esters was analyzed with gas chromatography in 759 Finnish boys and girls aged 3-18 years in 1980 and again in the same subjects in 1983 and in 1986. The mean percentage of linoleate (18:2 n-6) increased from 50.85% in 1980 to 52.60% in 1986, while there was a decrease in myristate (14:0), palmitate (16:0), and eicosapentaenoate (20:5 n-3). The percentage of oleate (18:1) did not change. The stability (tracking) of cholesteryl ester fatty acid composition was examined by calculating linear correlation coefficients among the percentages of each fatty acid at the three study points. For linoleate, 3- and 6-year tracking correlations were 0.59-0.61 and 0.50, respectively; they were of about the same magnitude for arachidonate (20:4 n-6) and lower for the other fatty acids. Results indicate that the serum cholesteryl ester fatty acid composition has somewhat lower tracking than the total cholesterol concentration. The changes in the mean fatty acid composition of the study population obviously reflect a shift from saturated to unsaturated dietary fats.