ENT Nose and paranasal sinuses a29b745f Most common sinus involved in acute sinusitis? A Ethmoid B Maxillary C Sphenoid D Frontal High-Yield Explanation The sinus most commonly involved is the maxillary followed in turn by ethmoid, frontal and sphenoid. (Ref: Diseases of ENT, PL Dhingra, 7th edition, of no. 213)