194 clinical, laboratory, electrophysiologic, histological, histochemical and immunohistochemical parameters were studied through statistical analysis in 112 cases of Duchenne muscular dystrophy (DMD) and in 26 cases of Becker muscular dystrophy (BMD). It was found a significant statistical difference (p < 0.05) between the two groups concerning the age of evaluation, beginning of symptoms, difficulty in walking, running, climbing and going downstairs, frequent falling down, support to walk, localized muscle pain, stopping climb stairs, and inability to walk. Muscle biopsy showed statistically significant (p < 0.05) differences between the two groups regarding the intensity of connective tissue and focal adipose tissue proliferation, presence of diffuse rounded atrophic and angulated fibers, diffuse hypertrophic and splitting fibers. There were also differences regarding excessive internal fibers nuclei, hypertrophic types 1 and 2 fibers, angulated atrophic fibers and focal increasing in the NADH-TR, angulated atrophic fibers in non-specific esterase, and accumulated NBT in the periphery of fibers in succinic dehidrogenase. Isolatedly muscle biopsy gave the correct diagnosis in 52.7% of DMD cases and in 69.2% of BMD cases. Dystrophin detection by immunofluorescence (60 cases) showed: absence in 87.0% of fibers in DMD cases, and sarcolemmal membrane discontinuites in all BMD cases. The muscle biopsy diagnosis had an agreement with the dystrophin results in 82.6% of DMD cases and 71.4% of BMD cases.