To elucidate the clinical characteristics of aged patients with Becker muscular dystrophy (BMD), 4 patients with this disease who were over 50 years were examined. The ages at onset in all patients were later than 30 years. All were proven to have a deletion around exons 45-55 of the Duchenne muscular dystrophy (DMD) gene. Two patients became wheelchair bound in their 40s or beyond, while the other 2 (aged 73 and 69, respectively) were still able to walk at the time of examination. Three of 4 patients had no obvious hypertrophy in their calves, which is known to be one of the characteristic clinical features in the juvenile BMD patients. Serum creatine kinase levels were elevated in all patients, but not markedly (mean 444.8 +/- 230.3 U/l; normal value < 180 U/l). Dilated cardiomyopathy was clinically apparent in 2 patients. We emphasize that some BMD patients are free of muscular symptoms until their 50s and are still self-supporting in their 60s or 70s.