UNPREDICTED PREGNANCY AMONG CHILEAN young womenBackground: Unpredicted pregnancy is an evolution of the concepts undesired and unplanned pregnancy. It is more common among vulnerable strata of our society and related to lack of education. Aim: To explore the prevalence and social concomitants of unpredicted pregnancy among young women. Material and methods: Analysis of the databases of the Sixth National Youth Survey carried out by the Instituto Nacional de la Juventud in Chile during 2009. The universe corresponds to 7570 participants aged between 15 and 29 years, of both genders.  Results: Unpredicted pregnancy occurred in 43% of sexually active surveyed women. It was more common among women with a lower educational level and those aged 15 to 24 years, especially during the onset of active sexual life. There was also an inverse relationship between the degree of education, the use of contraception and the age when sexual activity starts. Conclusions: Unpredicted pregnancy is frequent among teenagers and more common among less educated individuals. The frequency of use of contraception is associated in greater measure to the degree of education rather than the age of onset of sexual activity.