The incidence of invasive fungal infections is increasing in parallel with an increase of patients with immunodeficiencies. Resistance to these drugs is becoming a problem in spite of increased and improved treatment options.Literature retrieved from Medline and personal findings and experience form the basis for this article.Candida albicans is still the most common species causing invasive fungal infections, but Candida non-albicans species are increasing in number. Invasive Aspergillus infections and infection with other moulds than Aspergillus spp. do occur, but do not constitute a large proportion of these infections. As of today we have four classes of antifungal agents and seven drugs with different mechanisms of action are registered in Norway. Primary resistance to several of these drugs has been observed in a number of Candida and Aspergillus species and this is the dominating form of resistance we observe today. Secondary resistance due to treatment is still an uncommon finding. Clinical resistance, which, in spite of in vitro susceptibility does not lead to eradication of the fungus, is also commonly observed.The incidence of natural resistant fungi is increasing. Our main current challenge is therefore to rapidly and precisely identify the fungi so the proper drug is used to quickly initiate treatment on the correct indication.