The rate of preterm births is very high in Hungary; it was 8.9% of the total livebirths in 2010. Preterm birth (<37 weeks) has a considerable health impact, because it is responsible for 85% of infant mortality and morbidity as well as for numerous chronic diseses in the long-term. Many maternal and fetal diseases can be identified in the background, but in a number of cases, preterm labor begins unexpectedly, without any prodrome. Presumably, the socioeconomic background and the presence of harmful lifestyle factors are related to preterm birth in these cases. Tobacco smoking is the most frequent harmful health behavior. At national level, the rate of smoking during pregnancy was 14.4% in the last 13 years, but in some counties, this proportion mounted to 25%. In these counties, the prevalence of preterm births also exceeds the national average. This summary highlights the factors related to disadvantaged socio-economic status that can be responsible for the higher number of preterm birth cases.