Sixth grade girls (N = 224) were queried about their preparation for and expectations about menarche, their parents' roles in preparation, and their understanding of the biological basis of menstruation, characteristics of the menstrual cycle, menstrual hygiene, and menstrual-related physical and psychological changes. Although girls viewed themselves as prepared for menarche, and claimed they had discussed it with their mothers, their explanations of menstruation reflected at best incomplete howledge, and more typically a variety of misconceptions or ignorance. In attempting to explain menstruation, they tended to focus on one particular element of the process (e.g., eggs or blood or the uterus), and were not able to integrate the elements into a comprehensive whole. Girls' howledge of the location and function of reproductive structures was faulty, and most did not understand how they were interrelated. Girls associated a variety of negative physical and psychological changes with menstruation, indicating that although they had not yet learned the biology of menstruation, they already had learned and intemalized the cultural stereotypes and myths about menstrual symptomatology. In view of reports of high levels of sexual activity, often at very young ages, and without protection, and the high risk for acquiring sexually transmitted diseases, the failure to adequately educate girls about their own anatomy and physiology has serious implications.