Chrysotriones A (1) and B (2), two new 2-acylcyclopentene-1,3-dione derivatives, were isolated from the fruiting bodies of the Basidiomycete Hygrophorus chrysodon, and their structures were established by spectroscopic data and synthesis of compound 2. They represent the first examples of 2-acylcyclopentene-1,3-diones found in mushrooms and suggest an unprecedented biosynthetic pathway, starting from fatty acid derivatives. Initial tests indicated interesting antifungal activity of chrysotriones against Fusarium verticillioides, one of the common worldwide pathogens of cultivated plants.