INTRODUCTION: Around the world each year 10% to 15% of direct maternal deaths are associated with hypertensive disorders in pregnancy. Not only it can be devastating and life threatening for the mothers but also for the babies. Risks for the baby include poor growth and prematurity [1]. In low and middle income countries many public hospitals have limited access to neonatal intensive care, and so the mortality and morbidity is likely to be considerably higher than in settings where such facilities are available. Thus, the approach to the problem preeclampsia should include issues related to prematurity and its impact, since many of these babies develop definitive complications, constituting a major public health problem with social and economic repercussions. OBJECTIVES: To evaluate the prevalence of preterm births in a public hospital health of the city of São Paulo, checking its main causal conditions, focusing in particular on the importance of hypertensive disorders in its determinism. METHODS: This was a retrospective study of a consecutive series of preterm infants, defined as gestational age less than 37 weeks born at Maternity School Vila Nova Cachoeirinha, situated at the north of Sao Paulo City, in the period from 01/04 to 31/12/2011. The study population was classified according to three main groups of causal factors: spontaneous labor, premature rupture of membranes and elective preterm delivery. In this group was evaluated the specific participation of hypertensive disorders. RESULTS: The number of live births during the study period was 5302 babies. Among these 433 had gestational age less than 37 weeks, corresponding to a prematurity rate of 8.16%. Of all infants, 385 cases were included in the analysis. Regarding the causes of the onset of preterm labor found that 140 cases (36.4%) presented with spontaneous labor, 128 cases (33.2%) had premature rupture of membranes and 117 (30.4%) cases were born as a result of elective preterm delivery. In the latter group 88 cases (75.2%) had complications related to hypertensive disorders. Regarding the general population of premature infants, hypertension accounted for 22.8% of cases. CONCLUSION: We conclude that among the various obstetric problems, hypertensive disorders represent an important impact on preterm birth in our setting, considering that our institution is a reference to this type of care across the city of São Paulo. This knowledge is a fundamental tool to support the adoption of interventions that can detect groups at risk for hypertension in pregnancy, the promotion of follow-up to intercept severe cases and provide an efficient network of maternity care that may have neonatal intensive care units. This set of measures is essential to minimize the impact of this serious problem.