We wanted to evaluate factors associated with high costs after allogeneic haematopoietic SCT (HSCT). We collected all in-patient and outpatient costs during the first year after HSCT over 5 years, from 2003 to 2007. Mean 1-year costs per patient were h141 493 (95% confidence interval (95% CI) ¼ 125 019-157 967). Patients treated with non-myeloablative conditioning (NMC) had reduced costs, but patients treated with reduced-intensity or myeloablative conditioning had similar 1-year costs. Multivariate analysis showed that increased 1-year costs were seen in post-transplant complications: rejection (relative hazard (RH) 1.24, Po0.001), acute GVHD of grades III-IV (1.31, Po0.001) and invasive fungal infection (1.15, P ¼ 0.02). In addition, increased costs were associated with retransplantation (1.21, P ¼ 0.001), mesenchymal stem-cell therapy (1.26, Po0.001), unrelated donor transplants (1.20, P ¼ 0.002) and the need for G-CSF treatment due to poor engraftment (1.12, P ¼ 0.047). In patients without any of these risk factors, mean 1-year costs were h84 773 (95% CI ¼ 71 145-98 400) (n ¼ 51). With three risk factors, the cost increased to h249 775 (95% CI ¼ 166 824-332 727) (n ¼ 14). To conclude, major complications increased the costs of HSCT. Unrelated donor transplants were more expensive than HLAidentical sibling transplants. Costs were reduced in patients treated with NMC.