To describe the evolution of the prevalence of anemia in pregnant adolescents attended at a public maternity in the city of Rio de Janeiro from 2004 to 2013. A retrospective cross-sectional study with 628 pregnant/postpartum women divided into 3 groups: Group A (2004-2006), Group B (2007-2010) and Group C (2013). Information about anthropometric, clinical, sociodemographic data and obstetric and prenatal care of adolescents was obtained from medical records of the pregnant women. A hemoglobin concentration n<11 g/dL was considered to be anemia. Data were analyzed statistically by the chi-square test, Student's t-test and ANOVA, and the post hoc Tukey test. The prevalence of gestational anemia over the years was 43% (GA=138), 36% (GB=80) and 47.1% (GC=40) and the overall prevalence for the 2004-2013 period was 41.1% (n=258). The occurrence of anemic pregnant women increased with the progression of pregnancy; however, in the 3rd quarter there was a decrease in the prevalence of anemia in GB (29.3%) compared to GA (38.7%; p=0.04). Factors associated with anemia were number of prenatal visits and prenatal nutritional assistance, place of residence, pre-pregnancy BMI, and gestational weight gain. The results showed that the prevalence of anemia among pregnant adolescents seen at a public maternity is high. There was no reduction of anemia during the study period and other factors in addition to iron deficiency were involved in the genesis of anemia in this population.