Background Polyunsaturated omega-3 fatty acids may beneficially influence healing processes and patient outcomes.The aim of this research was to study the clinical efficacy of fish oil enriched total parenteral nutrition in elderly patients after colorectal cancer surgery.Methods Fifty-seven elderly patients with colorectal cancer were enrolled in this prospective,randomized,double-blind,controlled clinical trial.All patients received isocaloric and isonitrogenous total parenteral nutrition by continuous infusion (20-24 hours per day) for seven days after surgery.The control group (n=28) received 1.2 g/kg soybean oil per day,whereas the treatment group (n=29) received 0.2 g/kg fish oil and 1.0 g/kg soybean oil per day.Blood samples were taken pre-operatively,and at days one and eight after the operation.The plasma levels of CD4,CD8,CD4/CD8,interleukin 6 (IL-6) and tumor necrosis factor a (TNF-a) were measured.Clinical outcomes were then analysed.Results Patient characteristics were comparable between the two groups.At day eight post-surgery,IL-6,TNF-α and CD8 titres were lower in the treatment group when compared to the control group; these results reached statistical significance.In the treatment group,there were fewer infectious complications and incidences of systemic inflammatory response syndrome (SIRS),and shorter lengths of hospital stay were observed.The total cost of medical care was comparable for the two groups.No serious adverse events occurred in either group.Conclusions Fish oil 0.2 g/kg per day administrated to elderly patients after colorectal surgery was safe and may shorten the length of hospital stay and improve clinical outcomes.