If a candidate fails on the first attempt of the CEH exam, they can immediately test again when they feel ready. However, we definitely suggest taking time to review the domain areas you struggled with in order to increase your chances of passing on your next attempt. If you fail your retake of the Certified Ethical Hacker Exam, you will be required to wait a certain amount of time (between 14 days and 1 year) between each of your subsequent attempts. EC-Council's Exam Retake Policy details this waiting period.