We also investigate the acquisition and understanding of the concept of the menstrual cycle, as one of the most perfect and most complex biological systems. The study included 186 students of third grade grammar school from Split (122 girls and 50 boys and 14 undecided). The research was conducted through a combination of 4 tests of which three tests with graphs of different length of the menstrual cycle and no one test graph. Each test had 6 questions. Total resolve for determining the date of ovulation was 67.39% if compared to the result of gender was determined that no significant difference in the results of boys and girls. The research evidence that there was a resolve for ovulation was very low and amounted to 14.49%, which indicates a coincidence choosing the date of ovulation. The analysis phase with the highest level of female sex hormones, a total of 34.78% of the students answered correctly and read out from the graph and values. The analysis of the lowest levels of female sex hormones resolved a total of 56.16% of the students. A link between low levels of female hormones and re menstruation recognized the 68.12% students. From all the research was a poor attainment and understanding of the concept of the menstrual cycle, from which it is clear that of lectures and passive approach students should be replaced with more modern curricular approaches in biology.