Mushrooms and mushroom products are very popular in many countries around the world. However, these food products can be a source of biogenic amines, due to the content of precursors of these compounds and the high susceptibility to microbiological spoilage. Biogenic amines have a significant impact on food quality and may pose a threat to human health. The presence of spermidine, putrescine, tyramine, cadaverine, histamine, spermine, and agmatine was determined for the first time in 53 processed and unprocessed mushroom products available on the Polish market. The results showed a high variation in the content of biogenic amines in the individual products, depending on the producer. Spermidine and putrescine were the main biogenic amines, as they were found in 47 and 39 types of mushroom products, respectively. Tyramine and cadaverine were found in 15 samples of processed mushrooms. Histamine was present in only eight samples of dried Polish forest mushrooms; nevertheless, it was regarded a real threat to consumer health due to its very large quantities. It should be noted that dried mushrooms are intermediate products used after hydration as ingredients of various dishes, e.g. soups, sauces, stuffing; hence, the amount of histamine in the final product is substantially lower.