Aneurysmal bone cysts (ABCs) are benign, slow growing expansile lesions usually found in long bones or vertebrae. Plain radiography reveals expansion of bone and cortical thinning. MRI may assist in diagnosis by virtue of its ability to demonstrate blood-fluid levels, which is a characteristic finding in these lesions. Very few cases of ABC of the paranasal sinuses have been reported in the literature. We present MRI findings of ABC of the ethmoid sinus in a 19-year-old male.