BACKGROUND AND AIM OF THE STUDY: The quadricuspid aortic valve (QAV) is a rare congenital heart defect. All published cases of this rare malformation were reviewed. The study aim was to enlarge the evidence base for the condition, thus enabling conclusions to be drawn about its clinical course. METHODS: A literature search was conducted using the databases PubMed, Web of Science and the search engine Google. The reference sections of all relevant articles were also searched to identify additional cases of QAV. Cases with a truncal valve were excluded. RESULTS: A total of 186 cases was found. The mean age of patients was 50.7 years, and there was a slight male predominance (male:female ratio 1.61:1). Echocardiography was the leading mode of detection, followed by surgery, autopsy and aortography. Pure aortic regurgitation was found in almost 75% of cases, while only ca. 16% of the valves functioned normally. CONCLUSION: The QAV is a rare congenital heart defect with a high potential for serious complications. Patients with this condition should be carefully evaluated, and require close follow up.