Neonatal screening for Duchenne/Becker Muscular dystrophy (DMD/BMD) was begun as a pilot program on January 1, 1986. The aim of this program was to reduce the incidence of this X-linked recessive degenerative neuromuscular disease. The neonatal detection of a boy with DMD allows early identification of carriers and genetic counselling. This may avert the birth of other affected males born prior to clinical diagnosis of DMD in the propositus at about age 5 years. Between January 1, 1986, and December 31, 1988, we identified and characterized a cohort of 8 asymptomatic infant boys with grossly elevated levels of creatine kinase, an active primary dystrophic process of muscle and complete dystrophin deficiency. Five of 8 males have detectable DNA alterations involving the DMD/BMD locus. Based on current hypotheses, characterization of dystrophin expression of this cohort allows us to predict a DMD phenotype in all 8 boys. To date, no additional males with DMD have been born in these families. Prospective follow-up will allow us to test the validity of dystrophin testing in predicting the clinical course and impact of this program on reproductive decision making in these families.