While there have been considerable advances for ambulant children with Duchenne Muscular Dystrophy (DMD), no prospective study has so far been devoted to outcome measures in non ambulant patients, with increasing complaints from families and patients. This information appears to be relevant not only for a better understanding of the disease progression but also for possible enrolment of patients in future trials.As a result of an international effort, a new tool, the Performance of Upper Limb (PUL) was specifically designed to assess upper limb function in DMD boys. The purpose of the PUL is to assess changes that occurs in motor performance of the upper limb over time from when a boy is still ambulant to the time he loses all arm function when non-ambulant.The aim of the present study was to use the PUL in:(1)a cohort of typically developing children from the age of 3years onwards in order to identify the age when the activities assessed in the individual items are consistently achieved.(2)a cohort of DMD children and young adults to assess the range of findings at different ages.We collected normative data for the scale validation on 258 typically developing children from 3 to 14years old. A full score was consistently achieved (>85%) by the age of 3.5years. Below the age of 3.5years there was a significant number (>15%) who had difficulties in the items involving stacking cans, opening a Ziploc container, tearing a piece of paper and in lifting the heavier weights. After the age of 3.5years difficulties were only occasionally found in tearing a sheet of paper.When the PUL was performed in the 211 DMD patients (age range 2.8–23years), we observed a progressive deterioration of scores with age, with early involvement of the proximal muscles that was more obvious after the age of 10years. Even the oldest and weakest DMD patients were still able to perform some of the distal items, suggesting that the scale is capable of measuring small.