Background: Published randomized controlled trials (RCTs) on the efficacy of intranasal corticosteroid (INCS) in chronic rhinosinusitis (CRS) use either nasal delivery (nasal drop or nasal spray) or sinus delivery (sinus catheter or sinus irrigation) in patients with or without sinus surgery. This influences topical drug delivery and distribution. The effect of these factors on the published results of RCTs is assessed. This systematic review explores the strength of evidence supporting the influence of sinus surgery and delivery methods on the effectiveness of topical steroids in studies for CRS with meta-analyses. Methods: A systematic review was conducted of RCTs comparing INCS with either placebo or no intervention for treating CRS. Data were extracted for meta-analysis and subgroup analyses by sinus surgery status and topical delivery methods. Results: Forty-eight studies (3961 patients) met the inclusion criteria. INCS improved overall symptoms (standardized mean difference [SMD], -0.49; p < 0.00001) and the proportion of responders (risk ratio [RR], 0.59; p < 0.00001) compared with placebo. It decreased nasal polyp size with a greater proportion of responders (RR, 0.48; p < 0.00001) and prevented polyp recurrence (RR, 0.59; p = 0.0004) compared with placebo. Reduction of polyp size was greater in patients with sinus surgery (RR, 0.31; 95% confidence interval [CI], 0.20, 0.48) than those without (RR, 0.61; 95% CI, 0.46, 0.81; p = 0.009). Greater symptom improvement occurred when sinus delivery methods (SMD, -1.32; 95% CI, -2.26, -0.38) were compared with nasal delivery methods (SMD, -0.38; 95% CI, -0.55, -0.22; p < 0.00001). Conclusion: INCS is effective for CRS. Prior sinus surgery and direct sinus delivery enhance the effectiveness of INCS in CRS.