Substituted α-styrylcobalt(III)tetraphenylporphyrins rearrange to naphto(a,t)porphyrin derivatives, one carbon atom of the styryl fragment being bound to a pyrrolic position and an ortho carbon atom of a vicinal phenyl group. This unexpected result led us to reinvestigate the acid-catalyzed cyclization of 2-formyltetraphenylporphyrins, which produces the same naphtoporphyrin framework.