The objective of this article is to evaluate the impact of tuberculosis (TB) on perinatal outcome in a cohort of 25 pregnant women with TB treated at the National Institute of Perinatology (Mexico, City) from March 1990 to September 1995. They were compared with a cohort of normal pregnant women; both cohorts were matched by age, gestational age, and socioeconomic status. For purposes of analysis, patients with TB were further stratified into two groups: one included 9 women who started treatment either before or at the beginning of pregnancy, and the other constituted 16 women who started treatment in either the second or third trimester of gestation. Thirteen women (52%) had pulmonary TB, 7 (28%) had renal infection, and the rest of patients had diverse extrapulmonary localization of the infection. Obstetrical morbidity and neonatal mortality were significantly higher in pregnant women with TB who started treatment late in pregnancy. Perinatal morbidity was similar in pregnant women receiving antituberculous drugs early during pregnancy to that in uninfected women. We conclude that TB represents a risk factor for pregnancy. Early treatment of the disease during gestation reverts its negative impact on perinatal outcome.