Background: The aim of our study is to systematically review the existing evidence on the role of corticosteroids in patients undergoing functional endoscopic sinus surgery (FESS). 
Methodology: Systematic search of MEDLINE (1950- 2014), EMBASE (1980-2014), metaRegister, Cochrane Library and ISI conference proceedings was carried out. 
Results: Eighteen randomised controlled trials with 1309 patients were included. Use of local and/or systemic corticosteroids with FESS was reported in four categories; operative, anaesthesia related, post-operative outcomes and risk of recurrence. Metaanalysis for operative outcomes demonstrated that, mean operative time (MD -10.70 minutes; 95% CI -15.86, -5.55; P <0.0001) and mean estimated blood loss (MD -28.32 mls; 95% CI -40.93, -15.72; P <0.0001) was significantly lower; and surgical field quality (MD -0.81; 95% CI -1.32, -0.30; P = 0.002) was significantly better in corticosteroid group. Meta-analysis showed that post-operative endoscopic scores (SMD -0.39; 95% CI -0.60, -0.17; P = 0.0004) were significantly better in corticosteroid group compared to no corticosteroid group. There was no increase in risk of sinusitis (RR 0.64; 95% CI 0.32, 1.30; P = 0.22) between use of corticosteroids and no corticosteroids; There was no significant difference in recurrence risk of chronic rhinosinusitis (CRS) in mixed population studies (RR 0.77; 95% CI 0.35, 1.70; P = 0.52) between the two groups but analysis of studies reporting on chronic rhinosinusitis with nasal polyps (CRSwNP) (RR 0.64;95% CI 0.45,0.91;P=0.01) showed significant difference in favour of the corticosteroid group. 
Conclusion: Pre-operative use of local and/or systemic corticosteroids in FESS, results in significantly reduced blood loss, shorter operative time and improved surgical field quality. Studies are limited on the intra-operative use of corticosteroids to reduce postoperative pain. Postoperative corticosteroids improve postoperative endoscopic scores in CRS and recurrence rates in cases of CRSwNP.