We report a 44-year-old man presenting with left hemiparesis following influenza vaccination. The neuroimaging studies showed a large, contrast-enhancing brainstem lesion and multiple punctate lesions suggesting microhaemorrhages in both cerebral hemispheres. The patient showed a remarkable response to high dose steroid treatment. Detailed diagnostic studies failed to yield any results supporting inflammatory/demyelinating diseases, suggesting that influenza vaccination might have been associated with the clinical findings. Our case implies that vaccination might be related with a wide range of clinical syndromes, including brainstem encephalitis.