Muscular dystrophies are a group of genetic diseases characterized by progressive skeletal muscle weakness and muscle cell death with replacement of muscle cells by fibrosis and fat. The most common muscular dystrophy in children is Duchenne muscular dystrophy (DMD), which predominantly affects males. Historically, DMD has resulted in loss of ambulation between ages 7 and 13 years and death in the teens or 20s. The average age at diagnosis is 5 years, despite earlier onset of symptoms. Becker muscular dystrophy is similar to DMD but has later onset and slower, more variable progression of symptoms. Birth prevalence of DMD has been estimated at 1 in 3,500 (2.9 per 10,000) male births and Becker muscular dystrophy at 1 in 18,518 (0.5 per 10,000) male births. To estimate the population-based prevalence of Duchenne/Becker muscular dystrophy (DBMD) and describe selected clinical outcomes, CDC and investigators from the Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet) analyzed data for males born during 1983-2002 that were reported to the MD STARnet from four participating states. This report summarizes those findings, which indicated overall state-specific prevalences on January 1, 2007, of 1.3-1.8 per 10,000 males aged 5--24 years. Among MD STARnet subjects, more than 90% of males with DBMD aged >or=15 years used wheelchairs. Nearly 60%percnt; of males with DBMD born during 1983-1987 had survived through 2007, emphasizing the need to develop and implement programs that address lifelong needs of males with DBMD.