Isolated basilar artery dissection is a rare vascular pathology with varied clinical presentations and prognoses. We report a case of a 54-year-old woman, presented with subarachnoid hemorrhages (Hunt-Hess grade II). Brain computed tomography demonstrated a perimesencephalic pattern of haemorrhage. Magnetic resonance angiography revealed an isolated basilar artery dissection. Conservative treatment was performed. A complete resolution of the clinical symptoms occurs over a period of 30 days. There was no recurrent haemorrhage. On a follow-up magnetic resonance angiography three months later, a complete resolution of the intramural haematoma in the basilar artery was demonstrated. Some of the cases of basilar artery dissection with perimesencephalic pattern of subarachnoid haemorrhages could have a good prognosis, and could be treated conservatively.