The ambrosia beetle Platypus cylindrus was very common in stands of Platanus orientalis trees in Greece, infesting trees already infected by Ceratocystis platani. The fungus C. platani was isolated from 59% of adult beetles of P. cylindrus collected on the wing in a heavily infected stand of P. orientalis. Transmission of C. platani was demonstrated in 80% of P. orientalis seedlings challenged with P. cylindrus beetles, which were previously fed in cultures of the fungus. In most of the cases, the beetles had bored tunnels in stems, where abundant perithecia of C. platani were observed. Platypus cylindrus adults regularly visited artificially wounded P. orientalis trees in a natural stand. Although this ambrosia beetle normally infests stressed or dead trees, it appears to play a role as a vector of C. platani, especially by visiting wounded trees.