The irradiation product of acenaphthene and benzil described by Oliveri-Mandalà, Giacalone, and Deleo has been shown to have the structure (III) and not that of the cyclobutane derivative (II, R = H) originally proposed. The main product obtained by the action of acetic anhydride and sulphuric acid on (III) is not the result of an acetylation process, but is the sultone (IV).