This study aimed to analyze the repercussion of first sexual intercourse on the number of pregnancies and partners of teenagers with obstetric history in Teresina (PI), Brazil. This is a cross-sectional study with 464 young women selected by accidental sampling who gave birth at 15-19 years of age in the first four months of 2006 in six maternity hospitals of the municipality. Primary data was collected from May to December 2008 at the participants' homes after tracking them in the hospital medical records. The univariate and bivariate analysis were performed by descriptive statistics and Pearson's Correlation Coefficient Test or T-test, respectively. Tukey's post hoc test was used as post hoc test and significant variables on the bivariate analysis (p < 0.05) were also included in the multifactor analysis of variance model. Schooling (p < 0,001) and menarche's age (p < 0,001) influenced the age of first sexual intercourse and this, in turn, showed significant negative correlation (p < 0.01) with the number of partners and pregnancies of young women. Thus, the earlier the young women start sexual activity, the higher the number of pregnancies and sexual partners until the moment of their reproductive life. Thus, early first sexual intercourse had a negative repercussion on these variables.