Irregular menstrual bleeding may arise due to exogenous sex steroids, lesions of the genital tract or be associated with anovulation. Irregular bleeding due to oligo/anovulation (previously called dysfunctional uterine bleeding or DUB) is more common at the extremes of reproductive life, and in women with ovulatory disorders such as polycystic ovary syndrome (PCOS). In anovulatory cycles there may be prolonged oestrogen stimulation of the endometrium without progesterone withdrawal and so cycles are irregular and bleeding may be heavy. This is the rationale for using cyclical progestogens during the second half of the menstrual cycle, in order to provoke a regular withdrawal bleed. Continuous progestogen is intended to induce endometrial atrophy and hence to prevent oestrogen-stimulated endometrial proliferation. Progestogens, and oestrogens and progestogens in combination, are widely used in the management of irregular menstrual bleeding, but the regime, dose and type of progestogen used vary widely, with little consensus about the optimum treatment approach.