Seventy-eight pigs (40 boars and 38 castrates) were used in a growth trial to study the effect of high oil class FH sunflower seed on the long chain fatty acid composition of backfat in baconer pigs. Three diets were formulated to contain 18% protein, 1,0% lysine and 13,5 MJ/kg digestible energy. Diet A, the control, was a normal pig growth diet. Diet T1 contained 16% class FH sunflower seed (sunflower oil cake + sunflower oil). Diet B was similar to diet T1, but for the sunflower oil being substituted with tallow. Seven experimental treatments were used. In treatments A, B, and T1 the respective diets were fed from eight weeks of age until slaughter at 85 kg live mass. In treatments T2, T3, T4, and T5 diet T1 was fed ad lib. until the pigs were 45 kg, 55 kg, 65 kg, or 75 kg in live mass, respectively, from which point diet B was fed until the animals were slaughtered at 85 kg live mass. The linoleic acid content in the backfat of the pigs that received treatment T1 was 197% higher than that of pigs on treatment B, indicating an enormous effect of dietary fat source on backfat fatty acid composition. The substitution of diet T1 with diet B resulted in increased unsaturated backfat in the pigs as the point of substitution approached 85 kg live mass. The significant differences (P ≤0,01) in linoleic acid content between the experimental treatments suggest the possibility of manipulating the fatty acid composition of backfat by strategically feeding diets containing fats with different levels of saturation. No significant differences were found in growth performance or efficiency between pigs receiving T1 and B and for treatments T2, T3, T4, and T5. Boars had a 12,5% higher (P ≤0,01) backfat linoleic acid content than castrates, probably resulting in a softer backfat.