Authors after a concise description of the disease, show some data about Infectious Haematopoietic Necrosis spreading in Italy. Since 1987, when the disease has been firstly diagnosed, 41 outbreaks have been virologically detected. The disease has been diagnosed in 22 trout farms in six different regions: Marche, Toscana, Lombardia, Veneto, Friuli and Trentino. Yolk-sac fry seems to be the most common host, with a mortality higher than 90%. In fingerlings and trouts the mortality never exceeded 10%. Authors underline the need for an IHN investigation all over the country , to verify the real diffusion of the disease and to make ready the most suitable control measures.