AbstractTreacher Collins Syndrome (TCS) (OMIM 154500) is a congenital, craniofacial disorder inherited as an autosomal dominant trait. The responsible gene for TCS,TCOF1, was mapped to 5q32‐33.1 and identified in 1996. Since then,TCOF1mutations in patients with TCS have been reported from Europe, North and South America, however, no TCS cases from an Asian country have been molecularly characterized. Here we report mutational analysis for 11 Japanese patients with TCS for the first time, and have identifiedTCOF1mutations in 9 of them. The mutations detected were various, but most likely all the mutations are predicted to result in a truncated gene product, known as treacle. One mutation frequently reported was included in our cases, but no missense mutations were detected. These findings are similar to those for the previous studies for TCS in other races. We have speculated about the molecular mechanisms of the mutations in most cases. Collectively, we have defined some of the characteristic molecular features commonly observed in TCS patients, irrespective of racial difference. © 2005 Wiley‐Liss, Inc.