Crystalline, microporous molecular sieves efficiently catalyse the selective decomposition of cumene hydroperoxide into phenol and acetone, both under batch (25 °C) and down-flow fixed-bed (60 °C) conditions; large-pore high-silica zeolites, mainly zeolite Beta and its metallo-silicate (B-, Fe- and Ga-silicate) analogues, are found to be particularly useful catalysts in this reaction giving ca. 92±3% phenol selectivity.