A survey was carried out among EBMT centers about the use of busulfan for conditioning in allogeneic stem cell transplantation. Of 109 responding centers, 106 used busulfan for conditioning, 102 in conventional myeloablative doses, and 93 in reduced doses (RIC). The route of administration was mostly intravenous, but ~10% of the centers gave the drug orally. The number of doses in i.v. administration varied and was in myeloablative conditioning mostly one (50 centers) or four (43 centers) doses a day. Seventeen of the 106 centers used pharmacokinetics for dose adjustment in myeloablative conditioning, nine in RIC. The details of pharmacokinetic monitoring varied markedly. Three quarters of the centers reported adjusting the dose based on obesity in myeloablative conditioning and about 60% in RIC. The most common method for dose calculation was ideal body weight + 0.25 × (actual body weight - ideal body weight). In conclusion, the present survey showed marked heterogeneity in the current practices of busulfan administration for conditioning. The impact of the heterogeneity is not well known. Due to this and the scarcity of support from controlled clinical studies, no clear guidelines can be presented, but some prevailing policies to be recommended were identified.