The percentage compositions of fatty acids in serum cholesteryl esters and phospholipids were analysed with gas chromatography in 759 nine- to 24-year-old Finns. The correlations of serum fatty acids with dietary fat intake data were calculated from a 48-h recall survey. The dietary P/S ratio had correlations of r = 0.50 and r = 0.40 with linoleate (18:2) in serum cholesteryl esters and phospholipids, respectively. The intake of fish and fish products correlated positively with the percentages of eicosapentaenoate (20:5 n-3) and docosahexaenoate (22:6 n-3) in both cholesteryl esters and phospholipids. Dietary intake of saturated fat correlated positively with the percentages of all saturated fatty acids in cholesteryl esters and with myristate (14:0) in phospholipids. The intake of monounsaturated fats did not correlate positively with serum monoenes. In conclusion, the dietary P/S ratio is well reflected in the fatty acid composition of serum cholesteryl esters and phospholipids, the intake of saturated fats less well, and the intake of monounsaturated fats not at all.