We report the clinical experience of 18 patients with the congenital form of myotonic dystrophy, the majority of whom were diagnosed during the neonatal period and monitored from 5 to 14 years. Prematurity associated with congenital myotonic dystrophy gives rise to the severest clinical manifestations. Among them, respiratory involvement is common and is the leading cause of death in the neonatal period. Weakness and foot deformities secondary to muscle involvement are the predominant clinical features of this group of patients from birth to age 3 or 4 years. Once muscle strength improves, learning disabilities and behavioral disturbances become the main clinical problems. All our patients, when tested after 5 years of age, had intelligence quotients under 65, clearly below the average intelligence quotient of their mothers (IQ = 80). There is no relationship between the degree of mothers' and patients' disease. No patient has presented problems with routine immunizations, and no complications were observed in the 7 patients who underwent surgery under general anesthesia. Among the surviving patients, no correlation can be established between severity of disease in the neonatal period and the magnitude of sequelae as teenagers. Mental and behavioral disturbances are the factors which mainly influence the long-term management and prognosis of this cohort of individuals.