Products of the photodimerization of acridizinium bromide (1) were analyzed by means of 1 H NMR spectroscopy. Upon irradiation in solution and in the solid state four distinct isomeric photodimers were identified, two of which may exist in enantiomeric forms which could not be distinguished. Solubilization of 1 in anionic micellar solutions affected the regioselectivity of the photodimerization: as compared to a homogeneous aqueous solution the yield of dimers exhibiting higher dipole moments was enriched in the reaction mixture.