Performance of a submerged hollow fiber membrane bioreactor (MBR) for treatment of hospital wastewater was investigated. The removal efficiency for COD, NH4+-N, and turbidity was 80, 93 and 83% respectively with the average effluent quality of COD <25 mg/l, NH4+-N < 1.5 mg/l and turbidity <3 NTU. Escherichia coli removal was over 98%. The effluent had no colour and no odour. The transmembrane pressure increased slowly during 6 months operation. No membrane cleaning operation was used and no sludge was discharged during the 6-month operation period. (C) 2003 Elsevier Ltd. All rights reserved.