Our study showed that for the adult population, the most costly complications were chronic GVH, CMV infections and febrile neutropenia. Analysis of drug treatment costs showed that drugs account for the lion's share of direct medical costs after hematopoietic stem cell (HSC) allograft transplantation. Antifungals (Fluconazole, Voriconazole) account for 50% of total costs, antivirals (Aciclovir, Valaciclovir, Ganciclovir) represent around 26% of total costs, mainly used for the prevention of CMV infections, and immunosuppressants (Ciclosporin, Tacrolimus) make up 6% of expenditure.