Objective: Assess the changes in Eustachian tube (ET) function (ETF) with balloon dilation of Eustachian tube (BDET). Study Design: Prospective cohort for repeated testing measures. Setting: Clinical research center. Patients: Eleven adults with at least one patent ventilation tube (VT) inserted for chronic ET dysfunction (ETD) and history of otitis media with effusion. Interventions: Subjects with evidence of moderate to severe ETD on the side with a VT underwent unilateral BDET. Main Outcome Measures: Changes in ETF parameters after BDET measured by Forced Response Test (FRT), Inflation Deflation Test (IDT), and Pressure Chamber test. Results: With the FRT at 11 ml/min, opening pressure (OP) decreased from 458 ± 160 to 308 ± 173 daPa and closing pressure (CP) from 115 ± 83 to 72 ± 81 daPa at the 3-month post-BDET visit. The IDT and Pressure Chamber test showed that the percentage of middle ear (ME) pressure gradient equilibrated with swallows improved from 28 ± 34 to 53 ± 5% for positive and from 20 ± 28 to 38 ± 43% for negative ME pressure. Images from the pre- and post-BDET functional CT scans did not show apparent changes in the anatomy. Comparisons of ETF test parameters pre- and post-BDET suggested that the ET was easier to open and stayed open longer after the procedure. However, during the limited duration of follow-up most subjects continued to have ETD, some requiring VT re-insertion after the study period. Conclusions: Adults with severe ETD may benefit from BDET, however ETD may not be completely resolved and patients may continue to need VTs.