The relationship of sinusitis and paranasal sinus mucoceles to optic neuritis (ON) remains a challenge for both the otolaryngologist and the ophthalmologist. Currently, ON is assumed to be a rare complication of paranasal sinus diseases. Three new cases of ON associated with paranasal sinus diseases are described. We postulate different pathophysiologic mechanisms of ON in our three patients: compression of optic nerve due to sphenoid mucocele in the first patient; extension of bacterial infection to the optic nerve in the second patient; and invasion of aspergillosis to the orbital apex in the third patient. We assume that the complete recovery of the patient’s vision in the second case resulted from surgery, which had been performed immediately. A timely operation could possibly have prevented permanent blindness in cases 1 and 3 as well. Optic neuritis can occasionally be a complication of bacterial and mycotic sinusitis or paranasal sinus mucoceles, especially if located in the sphenoid sinus and posterior ethmoids. The evaluation of paranasal sinuses using imaging techniques is necessary to diagnose the problem, and immediate surgery can prevent permanent sequelae in indicated cases.