Fold-In -- What's the greatest April Fool's joke ever? (Al Jaffee)
Back Cover -- Mad Redesigns the U.S. Map (Al Jaffee)
Not so much a true cover variant as much as an extra cover that just happens to be blank, some issues of #538 were available with this curious addition to Mad history. This outer cover had no interior printing or artwork, but the back cover featured the same Al Jaffee redesigning of the U.S. map. For an excellent explanation of what this was all about click over to Tom Richmond's blog.
<---- and click this for a larger view of absolutely nothing!