Premature birth is associated with substantial excess childhood mortality and morbidity and therefore represents an important public health problem worldwide. In the United Kingdom and other industrialised countries it is now the commonest cause of infant mortality. This review will outline the most recently available data for the incidence of premature birth at local, regional, national and international level, and compare them to previously published figures. Any variation in these incidences will be considered along with factors likely to account for these differences. Problems with data collection and analysis will also be discussed.