The objective of the study was to compare the effect of sinonasal surgery vs. medical treatment on asthma in patients with chronic rhinosinusitis with or without nasal polyps. We executed a PRISMA guidelines-based systematic search of the following databases: PubMed, CENTRAL, Embase, Scopus and CINAHL. The search ran from database inception until 26 Feb 2014. We included controlled clinical trials comparing surgical intervention with medical intervention in patients with chronic rhinosinusitis with or without nasal polyps. We included only English papers. We used a pre-defined data collection form. Two authors independently assessed study quality. We assessed directness of evidence and risk of bias using pre-defined criteria. Our search yielded 2004 original articles, six of which satisfied our inclusion criteria. One article was excluded from further review because no comparison could be made of the subgroup of operated asthmatic patients versus the non-surgical control group. Only one study used objective pulmonary function measurements in asthmatics undergoing sinonasal surgery and therefore had the highest directness of evidence. Also it had a low risk of bias. Patient characteristics, treatments and outcome measures varied across studies, as did the observed effect. Risk of bias was high in most studies. Patient characteristics, treatment and outcome measurement differed across studies, making a comparison of the effects difficult. There is a risk of publication language bias. There is insufficient evidence either for or against sinonasal surgery for asthma control as compared to medical treatment.