In the second half of the 20th century, the forested surface in northern Spain started to increase during a process of reforestation and the replacement of native forest. This reforestation was performed mostly by introducing monocultures of exotic coniferous species. One of the implications of intense forest exploitation and the introduction of new forest species is an increase in disease outbreaks. Because the genus Heterobasidion includes some of the most significant conifer pathogens in the world, surveys were conducted to collect and identify H eterobasidion isolates associated with diverse hosts within coniferous forests and plantations in the Basque Country, northern Spain. A total of 159 stands were surveyed, and 45 isolates were obtained from different trees. Based on sequencing of the internal transcribed spacer region of the ribosomal DNA, all collected isolates were identified as European H eterobasidion annosum s.s. (European P-type). Heterobasidion annosum was detected in 28.3% of the sampled stands, with the following distribution by host: Chamaecyparis lawsoniana (11.1%), P inus pinaster (2.2%), P . radiata (42.2%), P . nigra (2.2%), P . sylvestris (17.8%), P seudotsuga menziesii (17.8%) and P icea abies (6.7%). The spatial distribution of the population showed a high degree of clustering. This is the first report of H . annosum s.s. causing damage to forest plantations of Chamaecyparis lawsoniana, P inus pinaster, P . radiata, P seudotsuga menziesii and P icea abies in Spain. In the current context of forest pathosystems, the management practice of replacing susceptible forest species with resistant species is recommended.