This guidance addresses FDA’s current thinking regarding clinical development programs and trial designs for drugs to support an indication for the treatment of one or more dystrophinopathies: Duchenne muscular dystrophy (DMD) and related dystrophinopathies including Becker muscular dystrophy (BMD), DMD-associated dilated cardiomyopathy (DCM), and symptomatic carrier states in females. The most prominent pathology in dystrophinopathies is degeneration of skeletal and cardiac muscle leading to progressive loss of muscle function, respiratory and cardiac failure, and premature death. This guidance does not address the development of drugs to treat secondary complications of muscle degeneration in dystrophinopathies (e.g., drugs specifically for heart failure or pulmonary infections).