To find the variability of the biological processes linked to the menstrual cycle and sexual and reproductive health at the ages when the reproductive stage starts and finishes. To evaluate the real understanding that adolescent girls have about the biological processes of the menstrual cycle. To evaluate the prevalence of dysfunctions linked to the cycle which are mentioned by adolescents and women and their usual behaviour to cope with them, in particular those related to taking medication. To evaluate the possible effects of these habits on menstrual dysfunctions: diets to lose weight, smoking and drinking alcohol, and regular physical exercise. To describe variability in menstrual cycles during the last phase of the fertile stage, to evaluate the frequency of connected symptoms. To evaluate adolescent behaviour as regards sexuality, pregnancy prevention and STDs. To evaluate possible differences in all these aspects according to socioeconomic levels. To establish recommendations according to the results, which will serve as general guidelines in programmes of health education on menopause for teenagers and women.