Mushrooms have been used as components of human diet and many ancient documents written in oriental countries have already described the medicinal properties of fungal species. Some mushrooms are known because of their nutritional and therapeutical properties and all over the world some species are known because of their toxicity that causes fatal accidents every year mainly due to misidentification. Many different substances belonging to poisonous mushrooms were already identified and are related with different symptoms and signs. Carcinogenicity, alterations in respiratory and cardiac rates, renal failure, rhabidomyolisis and other effects were observed in toxicity studies with various species including edible and therapeutic ones. Proper identification is important to avoid accidents and toxicity studies are necessary to assure the safe use of mushrooms as food and for medicinal purposes.