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<i>Paulownia</i> species are fast growing trees native to China, which are being grown in managed plantings in several European countries for the production of wood and biomasses. In 2018, wilting, stunting, leaf yellowing, and collapse, as a consequence of root and crown rot, were observed in around 40% of trees of a 2-year-old planting of <i>Paulownia elongata</i> × <i>P. fortunei</i> in Calabria (Southern Italy). Two species of <i>Phytophthora</i> were consistently recovered from roots, basal stem bark, and rhizosphere soil of symptomatic trees and were identified as <i>Ph. nicotianae</i> and <i>Ph. palmivora</i> on the basis of both morphological characteristics and phylogenetic analysis of rDNA ITS sequences. Koch’s postulates were fulfilled by reproducing the symptoms on potted paulownia saplings transplanted into infested soil or stem-inoculated by wounding. Both <i>Phytophthora</i> species were pathogenic and caused root rot and stem cankers. Even though <i>P. palmivora</i> was the only species recovered from roots of naturally infected plants, in pathogenicity tests through infested soil <i>P. nicotianae</i> was more virulent. This is the first report of Phytophthora root and crown rot of a <i>Paulownia</i> species in Europe. Strategies to prevent this emerging disease include the use of healthy nursery plants, choice of well-drained soils for new plantations, and proper irrigation management.