The muscular dystrophies are a group of inherited disorders that are clinically and genetically distinct. Genetic counselling is an essential part of the management of these patients. Molecular genetic techniques, in particular positional cloning but also now candidate gene analysis, have allowed the beginning of an understanding of the molecular pathology of these conditions. This is most advanced in Duchenne and Becker muscular dystrophy, where the gene and protein responsible have been fully defined, and analyses of the gene and protein can offer specific diagnostic and prognostic information, as well as more precise carrier counselling. Gene localizations are known for Emery-Dreifuss muscular dystrophy, facioscapulohumeral muscular dystrophy, three forms of 'limb-girdle' muscular dystrophy, severe childhood autosomal recessive muscular dystrophy and Fukuyama muscular dystrophy. Closely linked markers for Emery-Dreifuss and facioscapulohumeral muscular dystrophy can be helpful in the investigation of large families with these conditions. Abnormalities of two different proteins associated with dystrophin in the muscle fibre have been shown in severe childhood autosomal recessive muscular dystrophy and Fukuyama muscular dystrophy. The application of the techniques of molecular genetics to the muscular dystrophies has had an enormous impact, from enhancing understanding of the theoretical background of these diseases, to direct implications in their clinical management. These advances are likely to continue.