The acidic degradation of diazepam in methanolic aqueous solution has been investigated. Apart from the known degradation products, 2-(N-methylamino)-5-chlorobenzophenone and glycine, produced by the hydrolytic cleavage of the benzodiazepinone ring, five novel products were isolated and fully characterized by their spectroscopic features and independent synthesis. Substituted 2-amino-3,5-dichlorobenzophenones and 2,4-dichloroacridinones were found, the formation of which in the reaction media is mechanistically intriguing. The role of these unexpected products in accelerated studies of diazepam stability is discussed.