Reversible cerebral vasoconstriction syndrome is caused by narrowing of cerebral arteries. The cardinal symptom is relapsing acute-onset headache also known as thunderclap headache, which may be accompanied by neurologic deficits. This is a case report of a 61-year-old woman with CT angiography-verified reversible cerebral vasoconstriction syndrome. We discuss the diagnostic work-up, i.e. lumbar puncture including test for xanthochromia and important brain imaging, differential diagnoses and treatment of the most important causes of thunderclap headache.