We have investigated the frequency of deletions in the dystrophin gene in 108 unrelated Duchenne and Becker muscular dystrophy (DMD/BMD) patients from southern Italy (DMD, n. 47; BMD, n. 61) and identified 89 deletions. The de novo mutation rate (about 30%), and the preferentially maternal origin of deletional mutations, analysed in families in which the maternal grandparents were available or their haplotypes could be unequivocally reconstructed, are in agreement with data reported for other populations. The correlation between BMD phenotype and type of deletion suggests that, in the distal rod domain region, the deletion size may not be as crucial as the particular combination of missing exons. In fact, we provide immunohistochemical and clinical evidence that in-frame deletion of the hinge III region in the distal rod domain results in a milder phenotype as compared with shorter deletions that do not include the hinge III region. Our data obtained in BMD patients, by confirming inferences arising from minigene transfection experiments in mdx mice, represent an important contribution to gene therapy approaches.