A 47-year-old man presented with abdominal pain, neck stiffness, severe transient hypertension and unusually dark urine. Cerebrospinal fluid investigations and angiography confirmed the diagnosis of a subarachnoid haemorrhage. Porphyrin studies on the patient and his family demonstrated that the family has acute intermittent porphyria. This is the second case report of an acute hepatic porphyria presenting with a subarachnoid haemorrhage. Acute transient hypertension during the attack of porphyria caused the rupture of an intracranial arterial aneurysm.