Frequent recurrent mutations of the human dystrophin gene lead to Duchenne and Becker muscular dystrophies. Although the approximately 2.5 Mb size of the gene may form a large target for mutations it is not clear to date which mechanisms promote the observed high frequency of spontaneous mutants (1 in 10,000 X-chromosomes) of which a high percentage (> 70%) are gross structural aberrations (deletions/duplications). In order to gain insight into possible molecular mechanisms we have cloned and sequenced the deletion junction fragments from two unrelated Duchenne patients. Our data, together with a short review on other cases from the literature, present evidence that errors of DNA replication may contribute to the generation of submicroscopic chromosome rearrangements.