Duchenne muscular dystrophy (DMD) is a disease of progressive muscular weakness and wasting. This study is designed to evaluate the muscle strength and functional performance of patients with DMD during the natural progression of this disease. This study comprises a sample of 35 subjects who were confirmed to have DMD. Manual muscle testing (MMT) was used to evaluate muscle strength, the Brooke functional scale to rate the motor function of the upper extremity, and the Vignos functional scale to rate the motor function of the lower limbs. The results showed a significant positive correlation between age and the decrement in strength, i.e. a one year increment in age led to a 3.9% decrease in the average muscle strength. The strength loss always occurred in a typical pattern proceeding from the lower extremities to the upper extremities, and from the proximal to the distal parts. There was a significant negative correlation between muscle strength and both the Brooke and Vignos functional scales. These findings may suggest that decreased muscle strength results in a progressive worsening of the functional performance of the extremities. In addition, the Brooke scale is significantly correlated with the Vignos scale through the natural course of DMD. The high percentage (90.5%) of subjects without the long leg braces needed for ambulation indicates an inadequate rehabilitation care for DMD patients in this country.