Objective: To evaluate the changes of late perinatal morbidity related to the decrease perinatal mortality. Design: Comparative epidemiological study. Setting: Institute for the Care of Mother and Child, Prague. Methods: Comparison of epidemiological national and international data on the relationship of perinatal mortality and late perinatal morbidity. Results: When the value of perinatal mortality was higher than 10 ‰ (in developed countries in 90’s of the previous century), the incidence of late perinatal morbidity, mostly characterised by the incidence of cerebral palsy and serious mental retardation evaluated in different periods after delivery decreased with the decrease of perinatal mortality. However, with the decrease of specific early neonatal mortality the late perinatal morbidity started to increase. This increase depends on the birthweight and on the selected criteria evaluating the relationship of perinatal mortality and long-term perinatal morbidity in different studies. On the other hand, the absolute number of newborns increases with the decrease of perinatal mortality and the number of infants with late perinatal morbidity decreases. Conclusions: When perinatal mortality is low, the decrease of specific early neonatal mortality leads to the increase of late perinatal morbidity. The extent depends on the birthweight and on the selected criteria. Absolute number of infants with late perinatal morbidity decreases.

        Key words: perinatal mortality, late perinatal morbidity, birthweight, comparative epidemiological study, morbidity criteria