The aim of this study is to evaluate the incidence of interstitial pneumonitis following fractionated total body irradiation conditioning for bone marrow transplantation with varying lung doses due to shielding technique and different dose-rates. Between 1987 and 2001, a total number of 105 patients have received total body irradiation conditioning for bone marrow transplantation for hematological malignancies at Gulhane Military Medical School. Twelve Gy fractionated total body irradiation was delivered in 6 fractions over 3 consecutive days with Co-60 teletherapy machine. Conditioning therapy included only cyclophosphamide (60 mg/ kg/day for two days) and total body irradiation. The median follow-up for patients was 12 months. Interstitial pneumonitis developed in 10 patients out of 105 patients (9.52%). The median total dose to lung was 9.60 Gy (8.88-10.90). The difference between total lung dose and interstitial pneumonitis was not significant. Pneumonitis development in the high dose-rate (>0.04 Gy/min) group versus low dose-rate (< or =0.04 Gy/min) group was statistically significant. Low dose-rate fractionated total body irradiation is a reliable conditioning program in bone marrow transplantation with effective lung sparing to avoid interstitial pneumonitis.