Cyclical vomiting syndrome (CVS) is a rare condition affecting ~3 in 100,000 children, with Caucasian but no sex predominance.

It is generally a disorder of childhood with symptom onset in pre-school or early school age. Adult cases (onset in 3rd to 4th decade) have also been reported. As patients are well between episodes, there is usually a delay in diagnosis (2-3 years in children, longer in adults), with frequent emergency department presentations. It is a diagnosis of exclusion. Diagnostic criteria have been published by various bodies including the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition, the Rome Foundation (Rome IV 2016 under functional gastrointestinal disorders) and also the International Classification of Headache Disorders (3rd edition beta version). This reflects the uncertainty about the pathophysiology of the syndrome, described variously as functional, psychiatric, neurological either epileptogenic or autonomic dysfunction, occurring in association with or triggered by cannabis use versus a migraine variant or as episodic symptoms associated with migraine.