We report 4 cases of toxic leucoencephalopathy after heroin inhalation. The clinical features, which usually occur some days or even longer after the last heroin consumption, are dominated by a cerebellar syndrome. The cerebellar hemispheres are almost always affected; the cerebral hemispheres, the cerebellar peduncles and the pyramidal tract may be affected. Vacuolar demyelination is the morphological substract of the lesions, which are symmmetrical, not contrast enhancing, hypodense on CT scan and hyperintense on T2-weighted MRI. The pathophysiology is unknown and seems different from post-anoxic leucoencephalopathy. The disease is usually progressive leading sometimes to death, but some cases show slow recovery.