BACKGROUND Acute sinusitis is a common reason for primary care visits. It causes significant symptoms and often results in time off work and school. OBJECTIVE We examined whether intranasal corticosteroids (INCS) are effective in relieving symptoms of acute sinusitis. METHODS We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library, 2008, issue 4) which contains the Acute Respiratory Infections Group's Specialized Register, MEDLINE (January 1966 to October 2008), EMBASE (1990 to October 2008) and bibliographies of included studies. METHODS Randomized controlled trials (RCTs) were considered eligible if they compared INCS treatment to placebo treatment of a control group for acute sinusitis; acute sinusitis was defined by clinical diagnosis and confirmed by radiological evidence or by nasal endoscopy. The primary outcome was the proportion of participants with either resolution or improvement of symptoms. Secondary outcomes were any adverse events that required discontinuation of treatment, drop-outs before the end of the study, rates of relapse, complications and return to school or work. METHODS Two review authors independently extracted the data, assessed trial quality and resolved discrepancies by consensus. RESULTS Four studies with 1943 participants met the inclusion criteria. The trials were well designed, double-blind, placebo controlled in which the included participants had acute sinusitis. The treatment assigned was INCS versus control treatment for 15 or 21 days. The rates of loss to follow up in the studies were 7%, 11%, 41% and 10%. When the results from the three trials included in the meta-analysis were combined, participants receiving INCS were more likely to have resolution or improvement of symptoms than those receiving placebo (73% versus 66.4%; risk ratio (RR) 1.11; 95% CI 1.04 to 1.18). Higher doses of INCS had a stronger effect on improvement or complete relief of symptoms: for mometasone furoate (MFNS) 400 mcg versus 200 mcg, (RR 1.10; 95% CI 1.02 to 1.18 versus RR 1.04; 95% CI 0.98 to 1.11). No significant adverse events were reported and there was no significant difference in the drop-out and recurrence rate for the two treatment groups and for groups receiving higher doses of INCS. CONCLUSIONS For acute sinusitis confirmed by radiology or nasal endoscopy, current evidence is limited, but supports the use of INCS as a monotherapy or as an adjuvant therapy to antibiotics. Clinicians should weigh the modest but clinically important benefits against possible minor adverse events when prescribing therapy.