Endoscopic sinus surgery (ESS) for patients with severe chronic rhinosinusitis (CRS) has become a well-established treatment in cases where medical therapy fails. Even though CRS patients are divided into two subgroups, CRS with nasal polyposis (CRSwNP) and CRS without nasal polyposis (CRSsNP), most studies present only results for the total cohort. This prospective cohort study evaluated the efficacy of ESS on both quality of life and olfactory function measures, in a cohort of Danish CRS patients diagnosed according to the EPOS criteria, with results analysed separately for the CRSwNP and CRSsNP subgroups. All 97 CRS patients who underwent ESS over an 18-month trial period were evaluated preoperative by SNOT-22 score, Sniffin' Sticks score, modified Lund-Kennedy endoscopic score and Lund-Mackay CT score. Patient outcomes were reevaluated at clinical follow-up 1 and 6 months postoperative. ESS efficiently and immediately improved quality of life for both CRSwNP and CRSsNP patients, with over 50 % reduction in SNOT-22 score 1 month after surgery, which sustained 6 months postoperative. Olfactory function measured by Sniffin' Sticks score showed overall improvement in both groups. ESS efficiently improved quality of life in both CRSwNP and CRSsNP patients, and surgery lead to an overall improvement in olfactory function. However, a minor proportion of patients experienced deterioration in olfactory function after ESS.