A prospective study of newborns whose mothers had untreated or inadequately treated syphilis was undertaken. The infants were followed up for 3-4 months to ascertain whether they had congenital syphilis. A number of variables were analysed as possible predictive factors for the development of congenital syphilis. A maternal Venereal Disease Research Laboratory (VDRL) titre of 1:32 or above indicated which infants would develop congenital syphilis with a sensitivity of 93% and a specificity of 78%. The risk of a congenitally infected infant was significantly higher amongst the group of untreated mothers (p = 0.036). Low birthweight per se did not appear to be a predictor of the subsequent diagnosis of congenital syphilis. Using these simple predictive factors it may be possible to determine which at-risk infants would most benefit from careful supervision or a full 10-day course of therapy.