Outpatient total body irradiation (TBI) as part of a comprehensive outpatient transplant program was delivered to 142 of 167 (85%) consecutive patients receiving TBI-based conditioning therapy. Outpatients received either a single fraction of 500 cGy (110 patients) or 1200 cGy in six fractions over 3 days (32 patients). Patients were assessed daily and were administered oral ondansetron and dexamethasone for prophylaxis of nausea and vomiting as well as i.v. hydration. Accommodation during outpatient TBI-based conditioning was either the patient's home if within 30 min of the hospital, a hotel on the hospital grounds or on a closed hospital ward. None of the 142 patients required admission to the inpatient program during their TBI. There was no difference in 100-day mortality between those receiving TBI as an outpatient (9%) vs as an inpatient (16%). Of four deaths occurring within the first 14 days post transplant, none could be attributed to receiving TBI as an outpatient. Two hundred and six inpatient days were saved through the delivery of outpatient TBI. A comprehensive outpatient program, appropriate patient selection, daily hydration, the use of prophylactic 5HT3 antagonist anti-emetic therapy all contribute to the safe delivery of outpatient TBI.