Implantable contraceptives allow safe and effective fertility regulation for up to 5 years. Currently available devices release low doses of progestogens. Disruption of vaginal bleeding patterns is almost inevitable, particularly during the initial months of use. Irregular and prolonged bleeding as well as amenorrhea are common. Irregular bleeding is unpopular with most women and unacceptable to some. This review describes the vaginal bleeding disturbances induced by modern implantable contraceptives and discusses the implications of these in terms of method use and discontinuations.The cause of the irregular bleeding is not fully understood, but recent evidence suggests that an increase in endometrial vascular fragility might precipitate vessel break-down and, hence, breakthrough bleeding. This review discusses this evidence and outline the possible mechanisms underlying breakthrough bleeding associated with implantable contraceptives. In addition, therapies for bleeding disturbances are described and their efficacy reviewed. (C) 2002 Elsevier Science Inc. All rights reserved.