The conformational properties and the stability of acylpyridinium intermediates formed in pyridine-catalyzed acylation reactions have been studied at the SCS-MP2(FC)/6-311+G(d,p)//MP2(FC)/6-31G(d) level of theory. It has been shown that stacking interactions can play a decisive role in the stability as well as the conformational preferences of these transient intermediates.