Background & Aim: Duchenne muscular dystrophy(DMD) which is caused due to the absence of cytoskeletal protein of dystrophin is the second most common, lethal genetic disorder in humans. The gene which is responsible for DMD is localized in the XP21 of human genum. Although genetic pattern and biochemistry of DMD have been recognized, pathophysiology that leads to disabling patients is not known. Patients & Method: On the other hand, there are not any scientific criteria for classification of DMD patients. Since muscle biopsy is the most important diagnostic method in this disease, we have tried to evaluate the intensity of the disease through clinical signs and histopathological findings and determine the most important variables involved in the progression of the disease. Results: This research was done on 51 DMD patients. Clinical signs and morphological findings on muscle biopsies were investigated. According to the clinical signs, the patients were classified into two groups: mild and severe. Doing different stainings on paraffin blocks of muscle specimens, we searched for some variables such as degenerating fibers, regenerating fibers, central nuclei, fibrosis, etc. The control group consisted of six orthopedic patients without any neuromuscular disorders who underwent internal fixation surgery due to traumatic fractures. Chi-square statistical method revealed a meaningful relation between disease intensity and pathological signs. Conclusion: Therefore, it can be concluded that the presence of some variables such as degenerating fibers, central nuclei, fibrosis, infiltration of fat and inflammatory cells can account for the progression of the disease and histopathological changes may be directly related to the intensity of clinical signs.