Clinical improvement following surgery in patients with Duchenne muscular dystrophy (DMD) may be influenced by the severity of muscle fiber damage. This study correlates morphometric alterations of muscle fiber types, severity of fat tissue proliferation and fibrosis with Western blots, multiplex polymerase chain reaction (PCR), and postoperative state in DMD. The main results of this study show that the mean diameter of type 2 fibers is usually markedly larger than that of type I fibers in DMD although the number of type 2 fibers is severely reduced. The mean percentage of the remaining type 1 fibers was in the range of 57-82%. The morphometric and histopathological results were in agreement with the clinically estimated postoperative state, especially in the patients who presented a severe state or suggestive clinical improvement. It is concluded that combination of both quantitative and qualitative evaluation of muscle biopsies is suitable for better evaluation of the postoperative state in patients with DMD, whereas severity of exon deletions correlated poorly with morphometry and postoperative clinical state.