Purpose: When first-line chronic rhinosinusitis (CRS) treatment fails, patients can either be treated with oral or injected systemic corticosteroids. Although the EPOS and international guidelines for CRS do not mention injected corticosteroids, it is commonly used by ear, nose, and throat specialists. While the risks of systemic corticosteroids, in general, are known, the pros and cons of injected and oral corticosteroids (OCS) in CRS treatment are unclear. Methods: A systematic review of studies that report the effects and/or side effects of injected and oral corticosteroids in the treatment of CRS was made according to the PRISMA guidelines. Results: Altogether, 48 studies were included, only five studies reported on injected corticosteroids, and five attended with side effects. Three studies found beneficial effects of OCS perioperatively on sinus surgery, while four articles found no effect. Nineteen articles reported that OCS resulted in an improvement in symptoms. Two articles presented a longer-lasting effect of injected corticosteroids than OCS. Three studies reported adverse side effects of systemic corticosteroids, while two studies showed no adverse side effects. One study showed less adrenal suppression after injected corticosteroids compared to OCS. The evidence is not strong but shows a positive effect of systemic corticosteroids that lasts longer with injections. Conclusion: Although systemic corticosteroids are widely used to treat CRS, there is a lack of studies comparing the OCS and injected corticosteroids. The evidence is sparse, however, injected steroids show longer effects with fewer side effects. An RCT study is needed to compare OCS and injected corticosteroids.