We evaluated the effect of the mother's age on the risk of unfavourable pregnancy outcome. The study considered 1348 190 first-born and 957 689 second-born babies born in Italy in 1990-94. The risk of stillbirth, preterm birth in liveborns, and low birthweight in liveborns at term, was first evaluated separately and then globally as a function of maternal age, education and parity. Older (> or = 35 years) mothers were found to run an increased risk, both on single and on global evaluation, with respect to their younger counterparts. Primiparae > or = 35 years of age, of low education, ran a global risk threefold higher (3.14 [3.02, 3.26]) than the young highly educated secondiparae who were the lowest risk (4.64% of babies at risk). From 26 years the global risk rose with each advancing year of maternal age, but parity and education modified the age effect. Linear fitting of the proportion of mothers > or = 35 since 1984 indicates that by the year 2025 about 25% of the mothers may face late child bearing.