A study of infants with bladder exstrophy or epispadias was based on data from ten malformation monitoring systems around the world. The material is derived from nearly 6.3 million births. The recorded prevalence at birth of bladder exstrophy was 3.3 per 100,000 births and of epispadias (without bladder exstrophy) 2.4 per 100,000. The recorded rates of bladder exstrophy did not vary between the monitoring systems, but the rates of epispadias did. Furthermore, nearly all registered infants with epispadias were males. The sex ratio for bladder exstrophy was 1.5:1. Perinatal deaths occurred mainly when other malformations were also present. There was an increased risk in this group of malformations in infants of women aged less than 20 years. At high parity (3+), an increased risk was observed for bladder exstrophy, but there was a decreased risk for epispadias. The birth weight distribution was shifted slightly more to the left in isolated bladder exstrophy than in isolated epispadias, but was considerably shifted to the left when other malformations existed with bladder exstrophy. Most infants with other malformations belonged to the cloacal exstrophy sequence. There was no definite time trend between 1970 and 1985 in the prevalence at birth of bladder exstrophy. The study demonstrates how data from different monitoring registries can be pooled to characterize a rare malformation.