The ACOG has recommended that the initial visit to an obstetrician‐gynecologist for health guidance, screening, and provision of preventive services should take place around age 13–15. At this visit, clinicians can provide guidance to young girls and their parents on adolescent physical development based on data that define parameters for normal pubertal development, menarche, and menstrual cyclicity, and address menstrual hygiene and emerging adolescent concerns. Adolescent menstrual cycles are initially variable, but this variability does not imply that there are no useful parameters for menstrual cyclicity. Data indicate that cycles typically range from 21 to 45 days, even in the first few gynecologic years. Individuals with cycles that vary widely from this norm may have significant pathology, most commonly hyperandrogenism or polycystic ovary syndrome. Controversy now exists regarding the lower limits for the onset of pubertal development in girls; data suggest that pubertal growth may be occurring earlier than had previously been described. The age of menarche has remained constant. Clinicians can furnish information about menstrual hygiene and menstrual protection and provide parental and teen guidance with printed patient education materials and suggested Web‐based sources of information. The provision of anticipatory guidance and information to young girls and their parents can help ease the transition from childhood through puberty and a healthy adolescence.