The present study was performed to evaluate the effects of dietary n-3 and n-6 long-chain PUFA (LC-PUFA) on clinical outcome in a porcine model on early aortic vascular prosthetic graft infection (AVPGI). A total of eighty-four pigs were randomised to a 35 d dietary treatment with 10 % (w/w) fish oil (rich in n-3 LC-PUFA), sunflower oil (rich in n-6 LC-PUFA) or animal fat. After 3 weeks of dietary treatment, the pigs had an aortic vascular prosthetic graft inserted, and it was inoculated with Staphylococcus aureus (106 colony-forming units). Changes in selected plasma and erythrocyte n-3 and n-6 LC-PUFA concentrations and in plasma PGE2 metabolite concentration were determined in the 3-week preoperative period. Clinical signs of infection, i.e. rectal temperature, hindquarter function, general appearance and feed intake, were monitored daily in the 14 d post-operative period, and, finally, daily body-weight gain was determined in both periods. The preoperative changes in plasma and erythrocyte n-3 and n-6 LC-PUFA concentrations reflected the fatty acid compositions of the dietary treatments given, and plasma PGE2 metabolite concentration decreased in the fish oil treatment (P < 0·001). In the post-operative period, feed intake (P = 0·004) and body-weight gain (P = 0·038) were higher in the fish oil treatment compared with the sunflower oil treatment. The dietary treatments did not affect the number of days pigs were showing fever, weakness in the hindquarters or impaired general appearance. In conclusion, preoperative treatment with dietary fish oil compared with sunflower oil improved clinical outcome in pigs with AVPGI by improving feed intake and body-weight gain post-operatively.