5H-Dibenzo[a,d]cyclohepten-5-ones (I) ##STR1## (A and B being radicals for completing aromatic ring systems) are prepared by converting (Z)-2-(2-arylethenyl)arylcarboxylic acids (II) ##STR2## or E/Z-isomer mixtures thereof with a halogenating agent for carboxylic acids at from (-30.degree.) to +120.degree. C. to the corresponding carbonyl halides (III) ##STR3## where X is halogen, and cyclizing said carbonyl halides at from 0.degree. to 100.degree. C. in the presence of a Lewis acid.