Several medicinal mushrooms exhibit hypoglycaemic activities in vitro and in animal studies. In contrast to the high number of experimental results, only a few clinical trials and/or case reports have been published. They exist for mushrooms of the genera Agaricus, Coprinus, Ganoderma, Grifola, and Pleurotus. This article critically reviews these clinical investigations and describes which tasks need to be done to explore the potential of mushrooms for supportive treatment of type 2 diabetes.