Stereoselective formal synthesis of the diterpene tetraol (+)-aphidicolin (1) is described employing as key steps the cycloisomerization of the enyne 9 to provide the bicyclo[3.2.1]octane derivative 8 and the intramolecular Diels-Alder reaction of the triene 7 to form the aphidicolane-type ring system. This route is, in principal, highly stereocontrolled and extremely efficient.