PURPOSE: Duchenne/Becker muscular dystrophy (DMD/BMD) is an X-linked recessive disease caused by the mutation of dystrophin gene. Since the majority of mutations are deletions, recent diagnosis is made by the moleculargenetic tools. The authors summarized the clinical characteristics, and analyzed the moleculargenetic and immunohistochemical characteristics of DMD/BMD. METHODS: We reviewed the clinical and laboratory findings of 69 patients diagnosed as DMD/BMD from 1989 to 2000. Multiplex PCR using 26 primer sets was performed on 34 cases, and immunohistochemical staining using dystrophin antibody was done on 5 cases. Mutation profile and phenotype-genotype relationship were analyzed. RESULTS: 1) Mean age of onset was 3 years and 6 months. The presenting symptoms were motor weakness of the lower extremities, incidentally found elevated hepatic enzyme level, abnormal gait and motor developmental delay. Forty one percent had history of motor developmental delay, and most patients showed pseudohypertrophic calf muscles. Mean serum creatine kinase level was 11,232IU/L, and 44% revealed abnormal electrocardiogram. 2) All of the 63 cases showed typical histological findings of muscular dystrophy. Of the 5 cases with immunohistochemical staining, 2 showed complete (DYS1, 2 and 3) and 3 showed partial (DYS3) absence pattern. 3) Of the 34 cases on which multiplex PCR was performed, 14 showed deletions, and 11 of them had deletions between exon 44 and 55. CONCLUSION: Since the deletions were detected in less than 50% of the patients with multiplex PCR, tools for dystrophin protein expression must be combined for the correct diagnosis. Considering the invasiveness of muscle biopsy, we conclude immunohistochemistry should be followed in the cases with negative results in multiplex PCR, although moleculargenetic study is the primary diagnostic tool.