To identify the presence of bacterial biofilms on mucosal specimens from chronic rhinosinusitis (CRS) patients, and evaluate their relationship with severity of CRS.A prospective study of biofilms presence on 24 CRS patients compared with 12 controls was designed. The presence of biofilms was determined by scanning electron microscopy (SEM), and associations with the preoperative Lund–MacKay CT scores, Johansson endoscopic scores, and the history of ESS were assessed.Biofilms were found in 13/24 CRS patients (54.2%) but in only 1/12 controls (8.3%; P<0.01). CRS patients with and without biofilms had similar preoperative Lund–MacKay CT and Johansson endoscopic scores (P>0.05). Patients with revision ESS showed a tendency of higher biofilms incidence (5/7, 71.4%) than those undergoing their first procedure (8/17, 47.1%), but did not reach a significant difference (P>0.05).The higher incidence of biofilms in CRS patients suggests a role in the pathogenesis of CRS, but no correlation with severity of CRS.