Abnormal bleeding is a significant health problem, especially during adolescence and before menopause when anovulatory cycles are common. Curettage is rarely necessary to investigate or treat menstrual problems in adolescents, and its use should also be minimized in women younger than 40 years. In every age group, medical treatment is the initial choice, but surgical treatment by endometrial destruction or hysterectomy is sometimes required. Benign causes of bleeding include fibroids and possibly adenomyosis, but the indications for treatment in each case depend upon the extent of bleeding, not the extent of the lesion. Breakthrough bleeding (BTB) with combined oral contraceptives commonly leads to discontinuation of the method. As BTB tends to improve with time, in the first 3 months of pill use, unless there are obvious underlying causes, women should be reassured that it will likely settle. BTB is often the reason for discontinuing progestogen-only contraception, and there is a need for effective means of treating unscheduled bleeding. Bleeding occurs in approximately 3% of post-menopausal women, and the use of hormones increases the likelihood of bleeding by >5-fold. Knowledge of the underlying mechanisms of bleeding is essential to the development of effective treatment.