In a process for producing phenol and/or cyclohexanone, cyclohexylbenzene is contacted with an oxygen-containing gas to produce an oxidation effluent containing cyclohexylbenzene hydroperoxide and the cyclohexylbenzene hydroperoxide is then contacted with a cleavage catalyst to produce a cleavage effluent containing phenol and cyclohexanone. At least one of the oxidation effluent and the cleavage effluent also contains at least one by-product selected from phenylcyclohexanols and phenylcyclohexanones and the process further comprises contacting the by-product with a dehydration catalyst to convert the by-product to phenylcyclohexene and hydrogenating the phenylcyclohexene to cyclohexylbenzene. The dealkylation and hydrogenation may be conducted in a single stage.