Objective. To determine changes in peri-and neonatal care concerning neonatal mortality and morbidity by comparing 2 cohorts of very prematurely born infants (gestational age [GA] < 32 weeks),1 from the 1980s and 1 from the 1990s. Methods. The Leiden Follow-Up Project on Prematurity (LFUPP-1996/97),a regional,prospective study,includes all infants who were born alive after a GA < 32 weeks in 1996 and 1997 in the Dutch health regions Leiden,The Hague,and Delft. The Project On Preterm and Small for Gestational Age Infants (POPS-1983),a national,prospective study from the presurfactant era,includes all liveborn infants < 32 weeks’GA and/or < 1500 g from 1983 (n=1338). For comparison,infants from the POPS-1983 cohort with a GA < 32 weeks from the same Dutch health regions were selected (n=102). Results. The absolute number of preterm births in the study region increased by 30% :102 in 1983 to on average of 133 in 1996-1997. Centralization of perinatal care improved:the percentage of extrauterinely transported infants decreased from 61% in 1983 to 35% in 1996-1997. A total of 182 (73% )-of the LFUPP-1996/97 infants were treated antenatally with glucocorticosteroids compared with 6 (6% ) of the POPS-1983 infants. A total of 112 (42% ) of the LFUPP-1996/97 infants received surfactant. In-hospital mortality decreased from 30% in the 1980s to 11% in the 1990s. Mortality of the extremely preterm infants (< 27 weeks) decreased from 76% to 33% . The incidence of respiratory distress syndrome remained the same:～ 60% in both groups. Mortality from respiratory distress syndrome,however,decreased from 29% to 8% . The incidence of bronchopulmonary dysplasia increased from 6% to 19% . For the surviving infants,the average length of stay in the hospital and the mean number of NICU days stayed approximately the same (～ 67 days total admission time and 44 NICU days in both groups); including the infants who died,the mean NICU admission time increased from 27 days in the 1980s to 41 days in the 1990s. Equal percentages of adverse outcome (dead or an abnormal general condition) at the moment of discharge from hospital were found (± 40% in both groups). Conclusions. An increase in the absolute number of very preterm births in this study region was found,leading to a greater burden on the regional NICUs. Improvements in peri-and neonatal care have led to an increased survival of especially extremely preterm infants. However,increased survival has resulted in more morbidity,mainly bronchopulmonary dysplasia,at the moment of discharge from the hospital. Objective. To determine changes in peri-and neonatal care of neonatal mortality and morbidity by comparing 2 cohorts of very prematurely born infants (gestational age [GA] <32 weeks), 1 from the 1980s and 1 from the 1990s. Methods. The Leiden Follow-Up Project on Prematurity (LFUPP-1996/97), a regional, prospective study, includes all infants who were be born alive after a GA <32 weeks in 1996 and 1997 in the Dutch health regions Leiden, The Hague, and Delft. The Project On Preterm and Small for Gestational Age Infants (POPS-1983), a national, prospective study from the presurfactant era, includes all liveborn infants <32 weeks’GA and / or <1500 g from 1983 (n = 1338). For comparison, infants from the POPS-1983 cohort with a GA <32 weeks from the same Dutch health regions were selected (n = 102). Results. The absolute number of preterm births in the study region increased by 30%: 102 in 1983 to on average of 133 in 1996-1997. Centralization of perinatal care improved: the percentage of extrau A total of 182 (73%) -of the LFUPP-1996/97 infants were treated antenatally with glucocorticosteroids compared with 6 (6%) of the POPS- 1983 infants. A total of 112 (42%) of the LFUPP-1996/97 infants received surfactant. In-hospital mortality decreased from 30% in the 1980s to 11% in the 1990s. Mortality of the extremely preterm infants (<27 weeks The incidence of respiratory distress syndrome remained the same: ~ 60% in both groups. Mortality from respiratory distress syndrome, however, decreased from 29% to 8%. The incidence of bronchopulmonary dysplasia increased from 6 The average length of stay in the hospital and the mean number of NICU days is about the same (~ 67 days total admission time and 44 NICU days in both groups); including the infants who died , the mean NICU admission time increased from 27 days in the 1980s to 41 daysin the 1990s. Equal percentages of adverse outcome (dead or an abnormal general condition) at the moment of discharge from hospital were found (± 40% in both groups). Conclusions. An increase in the absolute number of very preterm births in this study Improvements in peri-and neonatal care have led to an increased survival of especially extremely preterm infants. However, increased survival has resulted in more morbidity, primarily bronchopulmonary dysplasia, at the moment of discharge from the hospital.