The enantioselectivity of the di-pi-methane photorearrangement was studied in chiral crystals. Achiral dibenzobarrelene acids 1 and 2 were forced to crystallize as chiral crystals by salt formation with chiral amines. Photolysis of these salts in the solid state yielded photoproducts in > 95% enantiomeric excess. The absolute configurations of the salts and their photoproducts were determined. This allowed the absolute steric course of the di-pi-methane reaction to be mapped and the structural features that control the enantioselectivity to be identified. In contrast to the solid state photolyses, irradiations in solutions give only racemic photoproducts, presumably because the salts dissociated.