The purpose of this study was to determine the association and its magnitude between prematurity and folate deficiency in women in their third trimester of pregnancy, and at labor. An incident case-control study was conducted using 2 controls per case. Data was obtained in a tertiary hospital in Valencia, Venezuela. A total of 543 women who delivered between May and December 1996 entered into the study. Women having a preterm delivery (< 37 weeks of gestation at delivery) were defined as cases (n = 181). Anemia was defined according to WHO as Hb less than 11 g/dL, when a pregnant woman had a folate serum level < 3 microg/ml was considered a folate deficiency. Logistic regression was used to analyze the data and likelihood ratio test was done for model comparison. Folate deficiency was found to be significantly associated with prematurity (Odds Ratio: 1.97; 95%CI = 1.06 to 3.68 P = .032), after adjusting for prior preterm labor, prenatal care visits, prior abortion, prior fetal death, placental abruption, and premature rupture oval membranes. In conclusion, maternal folate deficiency at the end of the third trimester of pregnancy, at labor, was associated with an increased risk of prematurity.