The relationships between short-term oral paracetamol treatment during pregnancy and mean gestational age and birthweight, in addition to the prevalence of preterm birth and low birthweight were estimated using newborn infants in the population-based large dataset of the Hungarian Case-Control Surveillance of Congenital Abnormalities between 1980 and 1996. Gestational age and birthweight were medically recorded. Of 38 151 newborn infants, 173 were born to mothers who had paracetamol treatment during pregnancy. A 0.4-week increase in the mean gestational age was found among exposed relative to unexposed, and with the use of paracetamol during pregnancy there was a significant reduction in the proportion of preterm birth (3.5% vs. 9.2%) (adjusted P = 0.01). The possible preterm birth protective effect of paracetamol may be associated with paracetamol-induced reduction of prostacyclin production in pregnant women. The clinical relevance of these findings needs further studies.