OBJECTIVES: To analyze the cost of treating invasive fungal infections (IFI) in stem cell transplant patients. METHODS: Prospective observation cost study from the hospital point of view  was performed in the major hematology clinic in Sofia for one year period. Bottom up cost analysis for the consumed health care resources and their cost was performed for all stem cell transplant patients. Medical resources included in the analysis was the clinical tests, medical devices, transplantation procedure, medicines, blood and blood formulating products, conditioning regime and cost of hospital stay. Cost of the resources was taken from the hospital tariff and insurance fund charges. Direct medical cost was calculated for the average transplant procedure and for the patients when IFI appears. RESULTS: Every patent with hemopoietic stem cell transplantation is considered for highly risky for fungal infection appearing due to suppressed immune system.  Antifungal prophylactic is obligatory for allogenic transplantation (n=27) and for susceptible patients with autologues transplantation (n=64). For allogenic transplantation prophylactic is performed with voriconazole and costs 3500 Euro. For the other patients usually fluconazole or itraconazole is used costing 1600 Euro. The total cost of allogenic transplantation from relative donor is 15000 Euro, for allogenic transplantation from non-relative is 25000 Euro and for autologues transplantation is varying between 10-20 000 Euro. Despite of prophylactics 3 IFIs were recorded during one year period and the cost of therapy rise to 50 000 Euro mostly due to increase in medicines cost to 66% of total cost.     CONCLUSIONS: The IFIs are twice increasing the average cost of hemopoietic stem cell transplantation mainly due to the increase in the cost of medicines to manage the infection.