The aim of this study was to evaluate the prevalence of preterm birth in the State of Santa Catarina, Brazil, and identify associated factors. Data were obtained from the SINASC database (Information System on Live Births). The quisquared test and Wald linear trend test between the dependent variable (prematurity) and the covariates were applied. Logistic regression was performed to evaluate the association between factors. In 2005, the preterm birth rate was 6.1% (95%CI: 5.9-6.2). Odds of prematurity were higher among mothers under 20 and over 40 years old, those with fewer prenatal consultations, and those undergoing cesarean sections. Prevalence of prematurity in Santa Catarina appears to be increasing. This scenario suggests the need to encourage prenatal care and discourage cesarean deliveries in order to decrease the prematurity rate. More studies using the existing databases could help identify their shortcomings and improve the quality of the data.