Premenstrual syndrome (PMS) and the perimenopause are each difficult conditions to manage. When they co-exist the difficulty is more than doubled. Understanding and recognising the differences and the similarities between these conditions should enable clinicians to provide appropriate treatment and significantly improve women's quality of life. Distinction between the two can be difficult. Anecdotally women seem more prone to PMS symptoms during the perimenopause, or at least they tolerate the symptoms less well. Symptoms of the perimenopause arise from falling oestrogen levels with irregular ovulation, resulting in symptoms of oestrogen lack and heavy irregular periods. Symptoms of the perimenopause are thus relieved by the administration of oestrogen. Premenstrual syndrome frequently results when ovulation occurs. PMS appears to be due directly to the progesterone produced following ovulation in women who have enhanced sensitivity to this steroid. Treatment can thus be achieved by suppressing ovulation or reducing progesterone sensitivity; the latter seems achievable by the administration of selective serotonin re-uptake inhibitors. Ovulation can be suppressed by a variety of methods and oestrogen is an approach which is frequently employed. This will also effectively treat menopausal symptoms. The main problem with using oestrogen is that a progestogen must be administered to prevent endometrial neoplasia; this can result in a return of the PMS symptoms. This article reviews the difficulties encountered in women with both disorders and provides a suggested management strategy.