To report a case of paranasal diffuse large B-cell lymphoma with orbital invasion extending to the intracranial lesion.

A 48-year-old male with chronic sinusitis visited our clinic for recent proptosis of his right eye, intermittent pain around the eyeball and headache. On a magnetic resonance image (MRI), a mass-like lesion was observed in the right frontal sinus, and its infiltration into the superior inner portion of the right orbital extraconal space and right intracranial dural space was suggestive of generalized inflammatory mucosal thickening in the paranasal sinuses. An incisional biopsy of the sinonasal tract was immediately performed. The pathology confirmed diffuse large B-cell lymphoma.

A mass involving the paranasal sinus and orbit can masquerade as chronic sinusitis. Because diffuse large B-cell lymphoma is rare and is a high-grade aggressive malignant lymphoma, the possibility for diagnosis must be considered.