Menstrual irregularity: The normal menstrual cycle is about four weeks long, and often follows the phases of the moon. Its length varies from three to seven days, but is usually consistent. However, girls and teenagers who menstruate are usually irregular. This is not a cause for concern unless regular menstruation has been established and is then lost. Some adult women also have irregular cycles. This can be a benign condition, but it can also be due to problems in the uterus or ovaries, including cancer. Adults with menstrual irregularity should see their physician to rule out disease or other problems. In some cases, medication can be used to regulate a chronically irregular cycle.