To determine the rate of low birth weight and some of the risk factors associated with this event among adolescents. A cross-sectional study conducted between October 1994 and December 2009 at a maternity in Campinas, in Brazil, using information generated from the computerized obstetric form. After selection of adolescents who delivered at this hospital, two groups were created, with and without low birth weight, respectively. Relative risk and 95% confidence interval for all independent variables (risk factors) and the Χ2 test for some perinatal results were performed. The level of significance was set at 5%. During the study period, 24,000 births occurred at CAISM. Of these, 2,404 occurred among 2,357 teenagers (10.02%) and the frequency of low birth weight was 15.1%. Adolescent pregnancy recurred in 294 (8.2%). Age less than 15 years-old, anemia, smoking, and hypertension were not significantly associated with low birth weight. Antecedent of miscarriage and association with systemic lupus erythematosus increased the risk of low birth weight. Cesarean section and an Apgar score below seven were more prevalent among adolescents with low birth weight, and 85% of all adolescents had less than six prenatal visits. The prevalence of low birth weight is higher among adolescents than among adult women, and there was a large number of adolescents with less than six prenatal visits. The antecedent of miscarriage and the presence of systemic lupus erythematosus were risk factors associated with the occurrence of low birth weight among adolescents.33286-91