A retrospective study was performed in 613 singleton pregnancies born to mothers aged < or =19 years over a 4-year period to determine the relationship between maternal height and preterm delivery (<37 weeks). The pregnancies were grouped according to maternal height quartiles for comparison of maternal and infant characteristics, obstetric complications and pregnancy outcome. The incidences of preterm delivery and labour decreased from 17.5% and 15.6% respectively in the lowest quartile, to 8.5% and 7.1% respectively in the highest quartile, without any difference in the risk factors or major complications. In the pregnancies without major complications, which included 73.3% of the cases of preterm labour, the rate of preterm labour was significantly and inversely correlated with the height quartiles. In the newborns, gestational age, birthweight and crown-heel length increased with the higher quartiles, but the ratio between infant crown-heel length and maternal height (height ratio) decreased with the higher quartiles. Unlike birthweight and crown-heel length, the height ratio was not correlated with gestational age. Our findings suggested that the inherent risk of preterm delivery in teenagers was related to their immature physical development at the time of pregnancy, as reflected by the maternal height.