Prospective study investigating the incidence of concurrent Eustachian Tube dysfunction (ETD) in patients with CRS refractory to medical therapy, and the effect of Endoscopic Sinus Surgery (ESS) on ETD in this patient group. Prospective study of 57 CRS patients. Outcome measures were SNOT-22 and ETDQ-7 questionnaires, tympanometry and Valsalva manoeuvre recorded pre-operatively and at 3 and 9 months post ESS. There was a moderate positive correlation between pre-operative ETDQ-7 and SNOT 22 scores (r equals 0.5715, p less than 0.0001). 68% of patients recorded positive ETDQ-7 scores pre-operatively, mean equals 20.6 (SD plus or minus 10.34). Mean ETDQ-7 scores were significantly lower at 3 months; mean equals 11.4 (SD plus or minus 5.65) (P less than 0.0001) and 9 months mean equals 11.4 (SD plus or minus 6.15) (P less than 0.0001) following ESS. Type A tympanograms increased form 76.6% pre-operatively, to 94.5% at 3 months and 96% at 9 months. Reported positive Valsalva increased from 38% pre-operatively to 96% at 3 and 9 months. Mean ETDQ-7 scores were higher in the CRSwNP group; 24.34 (SD plus or minus 9.2) compared to the CRSsNP group; 18.11 (SD plus or minus 10.3), (p equals 0.6101). 16 patients in the cohort had existing diagnoses of asthma, of which 4 had documented aspirin sensitivity. The mean pre-operative SNOT-22 score in this overall subgroup was 64.81 (SD equals plus or mins 20.13) compared with 49.07 (SD equals plus or minus 21.37) in non-asthmatic patients (p equals 0.0168). We found a high incidence of concurrent ETD symptoms in patients with severe CRS, which improve following ESS. Further research is required to better understand the association between CRS and ETD in order to provide effective treatments.