Adolescent girls' menstrual-related beliefs and behaviors are examined from a developmental perspective. 2 studies, 1 cross-sectional and 1 longitudinal, were conducted. In the first, 639 girls in grades 5-6, 7-8, and 11-12 were seen. In the second, 46 pairs of girls were seen twice: all were premenarcheal at the first testing; at the second testing, one-half had begun to menstruate in the last few months and one-half were a matched premenarcheal comparison group. Girls answered questions on menstrual symptomatology, menstrual-related attitudes, and potential informational sources. 3 questions were asked in the present study: (1) What are the expectations for menstrual symptoms that girls hold prior to menstruation and when do these develop? (2) How do expectations for menstrual symptoms and beliefs relate to the actual experience of menarche? (3) What are the sources of information for menstruation and do they relate to subsequent menstrual-related behavior? First, as early as fifth grade, premenarcheal girls had clear expectations regarding menstrual symptoms; their expectation that cycle-related changes would occur paralleled the changes reported by adult and older adolescent women. Second, girls who had begun to menstruate reported experiencing less severe menstrual distress (less pain, water retention, negative affect, and behavioral changes, and more concentration) than the premenarcheal comparison group expected to experience. In addition, early symptom expectations were positively related to later-reported menstrual distress (pain, water retention, and behavioral change) in the changing-menarcheal-status group. Third, there were few changes in the amount learned from various sources as a function of menarcheal status. However, correlational analyses indicate that girls who learned more from male sources rated menstruation as more debilitating and negative than those girls who learned less from male sources. The importance of socialization in the emergence of menstrual distress and negative menstrual attitudes is discussed.