The article describes pregnancies and labors of five women with myotonic muscular dystrophy and their four severely involved infants, and reviews the pertinent literature. Three of the four neonatal cases died by 3 weeks of age of respiratory failure or aspiration; the fourth infant is now 4 months old and has respiratory and swallowing difficulties. The symptoms of myotonic dystrophy worsen during pregnancy. A high rate of fetal loss occurs due to spontaneous abortion, prematurity, and neonatal involvement with the disease. Prolonged labor has been described as a consistent complication, but the evidence does not justify this conclusion. Although many neonates with myotonic dystrophy are asymptomatic, severely affected newborns have a recognizable disorder unrelated to the severity of the maternal disease. The most common clinical manifestations in the neonate are arthrogryposis involving predominantly the lower extremilies, generalized hypotonia and weakness, and pharyngeal weakness. Less constant features include polyhydramnios, facial diplegia, diaphragmatic paralysis, respiratory failure, decreased motility of the gastrointestinal tract, congenital cataracts, and electrocardiographic abnormalities.