Cord blood units (n = 5500) stored at the London Cord Blood Bank, including 59 units transplanted into a high risk and heterogeneous group of patients, were analysed. Transplant outcome data was available for 44 patients with a median clinical follow-up of 14 months (range 3–44 months). Over 40% of the collected units were of ethnic minority origin with a median volume of 79 ml (range 40–240 ml) and a median total nucleated cell (TNC) count of 11·9 × 109/l (range 10·0–24·8 × 109/l). The average patient's weight was 28 kg (range 5–80 kg) and the median age was 8 years (range 0·7–40 years). The median number of nucleated cells infused was 4 × 107/kg (range 1·10–16 × 107/kg). Neutrophil engraftment of 0·5 × 109/l was observed in 33 (74±%) patients with an average time of 28 days (range 11–60). The Kaplan-Meier estimate of acute graft-versus-host disease (grade II >) at day 100 was 37 ± 7% and in 27 (62%) patients, it was grade I or absent. The overall survival and disease-free survival at 2 years was 49 ± 8% and 41 ± 8%, respectively. Two years after transplantation the survival rate was 69% and 54% for patients receiving a 6/6 or 5/6 HLA matched units, respectively. Infection was the main cause of transplanted related mortality in these patients.