Teenage, is a stage of the human being that implies changes in behavior and social status.It begins with pre-adolescence (period of physiological development in which reproductive functions mature, the first secondary sexual characteristics appear and the physiological maturation of sexual organs); where the achievement of sexual and reproductive maturity marks the beginning of puberty.The purpose of this chapter is to compare the changes of the sexuality, fertility and motherhood about teenagers between 10 and 19 years old, according to the first information in a survey from the North of Santander ( Colombia) and Táchira (Venezuela); the variables compared are: age of the first menstruation, knowledge of the menstrual cycle and fertile period, age of the first sexual relation, age of the first pregnancy, use of the preservative during the first relation, the first pregnancy happened with the first person who experienced the first relation, the comparative analysis is univariate and descriptive.The research shows that most of people from North of Santander and Táchira did not know the first menstruation or fertil period.The first relation is at the age of 15 which is the right age to live this experience, but there are a lot of teenagers under 15 and it is considered sexual abuse; about 60 % demonstrated that his or her couple did not use the condom during his or her first relation.Sexually active teens often use the contraceptives.As you can see there is a little knowledge about sexual education on teenagers.