The presence of the virus associated with La France disease in mushroom fruit bodies collected in 2009 from different farms located in Western and Central Poland was confirmed. The isometric virus-like particles were observed using electron microscopy. Double-stranded RNA was isolated from mushrooms exhibiting a wide range of disease symptoms including premature veil opening, brown-coloured mushrooms and loss of crop yield. The presence of dsRNA molecules (M1, M2 and L3) associated with La France disease was confirmed by RT-PCR and sequencing. The virus was found in 120 among 200 samples tested. The amount of infected samples indicated mass occurrence of La France disease which could be a threat to the Polish mushroom industry.