Osteogenesis imperfecta (OI) type I is caused by a reduction of type I collagen resulting from the presence of a non-functional COL1A1 allele (null-allele). Owing to the lack of mutant mRNA, genomic screening of the COL1A1 and COL1A2 genes is required to identify a causal mutation, which is a costly and time consuming endeavour. We have developed an alternative approach for confirmation of a suspected diagnosis of OI type I based on the detection of a COL1A1 null-allele. Here we report the application of this COL1A1 null-allele detection test for prenatal diagnosis in a patient with OI type I in which it was shown that the fetus had inherited the normal COL1A1 allele from his affected mother and would not be affected with OI.