Hypertensive encephalopathy is a syndrome consisting of headache, seizures, visual changes, and other neurologic disturbances in patients with elevated systemic blood pressure. Diagnosis based on clinical and radiological findings, which are not specific, may be difficult to establish. Furthermore, hypertensive encephalopathy may develop gradually even when blood pressure is lower than that of malignant hypertension. We present clinical, magnetic resonance imaging (MRI) and autopsy findings in a 43-year-old schizophrenic patient with unrecognised hypertensive encephalopathy, which was misinterpreted by MRI as a diffusely growing brain stem tumour. Increased blood pressure was recorded several times, but it was not properly controlled and treated either during his out-door psychiatric examinations or hospitalisation. At autopsy, generalised atherosclerosis, concentric hypertrophy of the left ventricle and arteriolonephrosclerosis were found in addition to microvascular fibrinoid necroses and thromboses in the brain and kidneys, which were almost certainly caused by arterial hypertension evolving from benign into malignant stage. We discuss the differential diagnosis and give a review of the literature.