Mate, a hot infusion of Ilex paraguayensis, is a beverage largely consumed in Southeast Latin America, including during pregnancy. To assess the effect of mate drinking during pregnancy on preterm and small for gestational age (SGA) birth, a cross-sectional study was done. From January 1st to December 31st, 1993, in the first 24 h after delivery, all 5304 mothers giving birth at the hospitals in Pelotas, Southern Brazil, were interviewed and several of their characteristics were gathered. Birthweight was recorded and gestational age at birth assessed using the Dubowitz score. All 5189 single births were analyzed. The prevalence of SGA and preterm birth was 8.0 and 9.1%, respectively. Mate intake at least once a week during the entire pregnancy period was reported by approximately 68% of the mothers. Crude analyses showed a 30% increase in the risk of SGA among daily mate drinkers compared with nonconsumers (prevalence ratio = 1.3; 95% CI 1.1-1.6), whereas no statistical association was detected with preterm births. After controlling for confounders, the significance of the association with SGA birth no longer held and the lack of association with prematurity remained unchanged. In conclusion, prevalence of daily mate drinking was high among pregnant women and, contrary to the hypothesis, no harmful effect on intrauterine growth or duration of pregnancy was detected.