Background and aim of the study: Reversible cerebral vasoconstriction syndrome (RCVS) is characterized by severe "thunderclap" headache, with or without associated neurological symptoms and neuroimaging findings of reversible vasoconstriction of cerebral arteries. Puerperium is a recognized precipitant, but the incidence of puerperal RCVS is unknown. We conducted a prospective study to assess incidence, risk factors and clinical features of RCVS. Material and method: Nine-hundred consecutive puerperae were prospectively enrolled within three days of delivery. Past medical history, basal demographic, anthropometric and biological variables were recorded. Trans cranial Colour Coded Sonography (TCCS) was performed to assess early signs of vasospasm in brain vessels. A structured telephone interview was planned in all subjects one month postdelivery. Results: Thunderclap headache was recorded in 8 subjects (0.9%) on the first visit. At the one month follow-up interview 27 more patients reported having had at least one episode of thunderclap headache. In these 33 (3.8%) patients the course was spontaneously benign. One patient presented to the Emergency ward with throbbing thunderclap headache three weeks after delivery. Diagnostic work-up ended up in the diagnosis of RCVS, the outcome was favourable Conclusion: In normally coursing pregnancies and after uncomplicated delivery the risk of puerperal RCVS is negligible (0.1%). On the other way thunderclap headache may occur in a measurable proportion of (3.4%), although in the vast majority of cases (33/34 = 97%) it is of benign course. Transcranial Doppler sonography may be helpful to pick up those cases in whom further neuroradiological investigation is warranted. (C) 2017 Elsevier B.V. All rights reserved.