Preterm birth occurs between 22 and before 37 weeks. Its etiology is multifactorial and is a major cause of perinatal morbidity and mortality. The objective was to determine the risk factors associated with preterm delivery in pregnant women Guillermo Almenara Irigoyen National Hospital from January to June 2010. We performed a retrospective case - control and descriptive. The case histories of patients and controls were reviewed and recorded in chips and processed with SPSS version 15. The results were 81 patients diagnosed with preterm birth, with statistical significance in the following variables: absence of prenatal care (OR 3.07, P> 0.05), pre-eclampsia (OR 20.86, P <0.001), premature rupture of membranes (OR 4.03, P> 0,005), multiple pregnancy (OR 5.64, P> 0.01), chorioamnionitis (OR 2.02, P> 0.1), place of birth: saw (OR 3.88, P> 0.05) and socioeconomic status (...