Abstract A description is provided for Valsa sordida . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. DISEASE: Valsa sordida is usually associated with Valsa canker of poplar twigs. Wounded trees, and trees injured by insects or attacked by other pathogens are more susceptible to infection. Development of Valsa canker is affected by environmental stress (Guyon, 1996; Tao et al. , 1984). Poplar canker caused by V. sordida has been studied in different countries (CMI Distribution Maps of Plant Diseases, 1977; Worrall, 1983; Wang et al. , 1981) The fungus can be often found in declining poplar stands together with another pathogen of poplar trees, Leucostoma niveum. Valsa sordida may also cause necrosis of willow twigs. HOSTS: Populus spp., Salix spp. and, more rarely, other woody angiosperms. GEOGRAPHICAL DISTRIBUTION: Africa: Morocco. Asia: Armenia, Azerbaijan, China, Republic of Georgia, India, Iran, Iraq, Israel, Japan. Kazakhstan, Korea, Russia (Tatarstan), Turkey, Turkmenia, Uzbekistan. Australasia: Australia (Victoria), New Zealand. Europe: Austria, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, France, Germany, Greece, Ireland, Italy, Netherlands, Norway, Poland, Portugal, Rumania, Russia, Slovakia, Sweden, Switzerland, UK, Ukraine, former Yugoslavia. North America: Canada (Alberta, British Columbia, Nova Scotia, Ontario, Québec, Saskatchewan). USA (California, Colorado, Michigan, Minnesota). South America: Chile. TRANSMISSION: Both conidia and ascospores are air-borne, especially under humid conditions. Yellow or orange exudation of conidia from conidiomata can be often seen after rain.