Haemophilia B is caused by coagulation defects in the factor IX gene located in Xq27.1 on the X chromosome. Identifi cation of mutations contributing to defective factor IX may be advantageous for precise carrier and prenatal diagnosis. We studied 16 patients from 11 families, consisting of 8 patients of the Malay ethnic group, of which 6 were siblings. Factor IX mutations have not been previously reported in the Malay ethnic group. The functional region of the factor IX gene was sequenced and mutations were identifi ed in either the exon or intronic regions in 15 of the patients. One novel mutation, 6660_6664delTTCTT was identifi ed in siblings with moderate form of haemophilia B. Mutations identifi ed in our patients when linked with disease severity were similar to fi ndings in other populations. In summary, this preliminary data will be used to build a Malaysian mutation database which would facilitate genetic counseling.