The role of parental ageing on the incidence of adverse pregnancy outcome is based on increased morbidity and obstetric problems during pregnancy and delivery in old mothers, and on the accumulation of spontaneous harmful mutations for continuous cell divisions during spermatogenesis in old fathers. The aim of this study is to estimate the impact of paternal and maternal ageing on the risk of adverse pregnancy outcome. From the group of 3,616,622 Italian singletons born in 1990-1996 we estimated the risks of stillbirth, preterm birth (<37 weeks of gestation) in live births, and low birth-weight (< 2.3 Kg) in live full-term births. The risks were estimated as a function of maternal and paternal ageing through logistic regression models, which included, as covariates, parity (1st, 2nd, > or =3rd) and family education (low, < or =8 years of schooling for both parents; high, >8 years for at least one parent). Parental ages were examined as quantitative (in one year classes) or categorical factors (in three classes: fathers 20-29, 30-39, > or =40; mothers 20-29, 30-34, > or =35). We found that, compared with 20-29-year old parents, mothers > or =30 years and fathers > or =40 years are at risk of adverse pregnancy outcome. The effects are more relevant for preterm births and greater in the least than in the most favourable birth conditions, i.e., in first-born children of less educated families than in second-born children of highly educated families. For the risk of a preterm delivery, the odds ratio is OR = 1.32 [1.28-1.36] in mothers aged 30-34 years, and OR=1.97 [1.88-2.07] in mothers 235 years in the least favourable conditions, and OR = 1.14 [1.10-1.18] and OR = 1.56 [1.22-1.27] respectively, in the most favourable conditions. The impact of paternal ageing is smaller but significant in fathers > or =40 years: for the risk of a preterm birth, the odds ratio is OR = 1.40 [1.33-1.47] in the least favourable conditions, and OR = 1.14 [1.08-1.21] in the most favourable conditions. This last, baseline risk might be indicative of a paternal genetic component associated with childbearing in advanced age.