Retained bullets and fragments following a civilian gunshot injury are quite frequent in practical neurosurgery. It is usually possible to extract the foreign body surgically, while rare cases are conservatively treated because of technical reasons. Conservative treatment may present complications, and a rare form of this presentation is migration of the bullet. A 20-year-old man presented with migrating bullet from a supratentorial to opposite infratentorial area. We consider that in the migrating bullet fragment cases, if there is no contraindication, the most reasonable treatment is its urgent surgical removal. This report reveals a supratentorial bullet migrating to the infratentorial contralateral area, and related literature considering the different mechanisms of migration is discussed.