Background Nevoid basal cell carcinoma syndrome(NBCCS)is a rare autosomal dominant disease characterized by a combination of development anomalies and a predisposition to tumour formation.Mutation of patched gene(PTCH),considered the molecular defect of NBCCS,in a Chinese NBCCS family was investigated in this study.Methods Genomic DNA was isolated from blood samples of all 12 members of this family.The mutated PTCH gene was screened by polymerase chain reaction amplification and di rect sequencing.Results A new mutation of 3 bp(GAT deletion)was found in all seven affected members of this family.This mutation caused one aspartate deletion in the fourth transmembrane domain of the PTCH protein located within the sterol sensing domain(SSD).This deletion was not found in any unaffected members of this family nor in 200 controI samples.Conclusions Our findings suggest that one 3-bp deletion in PTCH gene was the cause of nevoid basal cell carcinoma in a Chinese family through affecting the conformation and function of PTCH protein.