Abstract A description is provided for Tilletia controversa . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Aegilops, Agropyron, Alopecurus, Arrhenatherum, Beckmannia, Bromus, Dactylis, Elymus, Festuca, Holcus, Hordeum, Koehleria, Lolium, Poa, Secale, Triticum, Trisetum . DISEASE: Causes dwarf bunt of winter wheat, and occurs sporadically on many grasses. Occasionally infects winter barley. Infected plants develop chlorotic flecks at an early stage, are markedly stunted, and produce rather fat, persistently green ears with protuberant spikes caused by the bunt balls which fill the grain. As with T. caries (CMI Descriptions No. 719) and T. foetida (CMI Descriptions No. 720) the contents of the grain are converted to a mass of teliospores which constitute the bunt ball. GEOGRAPHICAL DISTRIBUTION: Europe (except Spain and UK); N. Africa, W. Asia, N. America, Argentina and Uruguay (CMI Map 297, ed. 2, 1968). TRANSMISSION: Teliospores are released when the grain is harvested and contaminate soil and seed. Soil-borne spores are the major source of inoculum for infecting crops which occurs between December and April in NW USA (43, 1295). Teliospores in bunt balls can remain viable in the soil for several years.