Birth defects are the leading cause of infant mortality in the United States and the fifth leading cause of years of potential life lost (1,2). Despite the substantial allocation of medical and nonmedical resources to the care and support of persons with birth defects, the economic costs of such defects have not been estimated accurately. Because estimates of the cost per new case of a birth defect represent the savings from preventing a case, an incidence-based approach enables assessment of the value of prevention strategies. This approach was used to estimate the cost of illness for cerebral palsy and for 17 of the most clinically important structural birth defects in the United States. This report uses data from California (adjusted to provide national estimates) and national data (Table 1) to estimate the costs of these 18 conditions occurring in the United States during 1992.