Thanks for your question! It is completely normal for some girls to have mild to moderate menstrual cramps and for others not to have any cramps at all. The medical word for this discomfort is called dysmenorrhea (pronounced: dis-men-oh-ree-ah). Menstrual cramps are caused by uterine contractions (when the muscles in the uterus tighten and relax allowing blood to leave the uterus). Some girls have mild cramps on the first day of their period and others experience cramps longer. However, if menstrual cramps are so bad that a girl misses school, sports or social activities, she should make an appointment with her health care provider.