We report two cases of optic neuritis with optic nerve enlargement on MRI. Both had a clinical course typical for optic neuritis but also had a neuroradiologic finding most commonly seen with optic nerve glioma or meningioma, which initially led to an incorrect diagnosis. We review the six previous reported cases of optic nerve enlargement in optic neuritis. Including our cases, six of eight reported cases were in children with severe initial visual loss. Optic nerve enlargement is a rare finding in optic neuritis that might be a subtype of optic neuritis.