We measured the prevalence and incidence of Becker muscular dystrophy in the Northern Health Region of England, UK. Patients were identified from the records of the Regional Neurological Centre and Muscular Dystrophy Group laboratories, Newcastle upon Tyne, and by writing to local doctors. We used cDNA probes and/or dystrophin immunolabelling of muscle-biopsy samples to prove the diagnosis of all cases. Results were compared with the known prevalence and incidence of Duchenne muscular dystrophy. 73 patients alive and resident in the Northern Health Region were identified, giving a prevalence rate of 2.38/100,000. This compares with a prevalence of Duchenne muscular dystrophy of 2.48/100,000. The cumulative birth incidence of Becker muscular dystrophy (at least 1 in 18 450 male live births) was about one third that of Duchenne muscular dystrophy (1 in 5618 male live births), suggesting that the disorder is more common than previously thought.