In recent years, the most important advances in the treatment of transplant recipients, patients with haematological neoplasm and critically ill patients have been accompanied by an increase in the incidence of common fungal diseases and the emergence of some less common ones. Although new techniques (e.g. galactomannan detection) and new antifungals have appeared, these opportunistic infections remain difficult to diagnose and have a high mortality. New diagnostic techniques could improve this outlook, although they are far from becoming available in daily practice.