Thunderclap headache (TCH) is a neurological emergency that warrants immediate and comprehensive diagnostic determination. When no pathology can be identified the condition is classified as primary TCH, which is considered benign and self-limiting. TCH has also been reported as the initial symptom of reversible cerebral vasoconstriction syndrome (RCVS), which subsumes a variety of conditions, inconsistently coined Call-Flemming syndrome, benign angiopathy of the central nervous system, drug-induced arteritis, or migrainous vasospasm. Serious complications such as borderline ischaemic stroke have been reported. Although no standardized treatment regime exists, one commonly described but unproven therapy is parenteral or oral application of the calcium channel blocker nimodipine. Here, we report on a case of RCVS, where a progressive course prompted intra-arterial application of nimodipine, which resolved vasoconstriction immediately. We discuss the use of intra-arterial nimodipine application as a potential emergency treatment for a complicated or treatment-refractory course of RCVS.