Duchenne Muscular Dystrophy is a severe neuromuscular disorder, that weakens arm muscles among other muscles. In order to remain independent as long as possible, new aids are developed to support arm function. To develop these aids, more information in needed on arm function. Therefore, this thesis examined arm function in boys and men with Duchenne Muscular Dystrophy, using questionnaires and biophysical outcome measures. The results showed that already at a young age arm function is restricted, and that during the course of the disease the amount of limitations increase. This coincides also with increased pain and stiffness levels. First limitations can be seen during activities with the shoulder (reaching), and later on movement with the elbow (drink) and hand (write) become more difficult. Muscle force, however, declines before activity limitations occur. As a result, muscle force measurements could be used for early diagnosis of upper extremity limitations. We also found that corticosteroid use and an active lifestyle positively influence arm function, and that pain, stiffness and the occurrence of scoliosis have a negative impact on arm function. Using these results new aids can be developed and clinicians can prescribe better treatments to preserve arm function.