I do not believe it is a prerec for CEH, I think it's just what EC-Council advises you should have prior to CEH attempts so that you are more successful. Edit... Right off their website, clearly states: "This course is a prerequisite for the CEH program." Use…
Many people take the CEH exam without first taking the official course or buying the official training. In such cases, EC-Council requires that the CEH candidate have 2+ years of verifiable professional InfoSec work experience.
In the pdf link posted by Grafixx01, there is "Prerequisites This course is a prerequisite for the CEH program." Is the information on the pdf wrong? :s
Only eccouncil can answer that definitively, but there is no other mention of prereqs anywhere else in the marketing material, and there has never been a cert required for ceh in the past.