The effects of anterior ethmoidectomy, alone or combined with antrotomy and uncinectomy, on nasal and sinus airflow patterns were investigated using computational fluid dynamics (CFD) analysis of computed tomography scan-based three-dimensional nasal model reconstructions. The velocity, pressure, and airflow distribution, and airflow pathlines were evaluated. In model I, operated and non-operated airways were compared. In model II, the maxillary sinus was artificially sealed to evaluate the effects of ethmoidectomy alone. For both models, CFD simulations showed that post-op middle meatus airflow patterns were strongly affected, with higher air velocity, lower pressure, and larger-sized vortices, and the overall middle meatus airflow was redistributed laterally into the sinus cavities and away from the septum and superior meatus. Airflow rates at other intranasal sites were unaffected. The increase in post-op maxillary ventilation is larger than those in normal sinuses and sinuses with accessory ostia. Uncinectomy and antrotomy affect only local airflow within the antrum. In conclusion, middle meatus endoscopic sinus surgery (ESS) increases air exchange between sinuses and the nasal airway, increases middle meatus airflow at the expense of superior meatal flow, and produces vortices in the antrum and ethmoid. However, both ethmoidectomy and antrotomy/ uncinectomy affect only local airflow, with negligible influence far from the operation site. These computed changes help us understand where dryness and mucus crusting is likely to occur following middle meatus ESS.