The number of open-label extension studies being performed has increased enormously in recent years. Often it is difficult to differentiate between these extension studies and the double-blind, controlled studies that preceded them. If undertaken primarily to gather more patient-years of exposure to the new drug in order to understand and gain confidence in its safety profile, open-label extension studies can play a useful and legitimate role in drug development and therapeutics. However, this can only occur if the open-label extension study is designed, executed, analysed and reported competently. Most of the value accrued in open-label extension studies is gained from a refinement in the perception of the expected incidence of adverse effects that have most likely already been identified as part of the preclinical and clinical trial programme. We still have to rely heavily on post-marketing safety surveillance systems to alert us to type B (unpredictable) adverse reactions because open-label extension studies are unlikely to provide useful information about these types of often serious and relatively rare adverse reactions. Random allocation into test and control groups is needed to produce precise incidence data on pharmacologically expected, or type A, adverse effects. Some increased confidence about incidence rates might result from the open-label extension study; however, as these studies are essentially uncontrolled and biased, the data are not of great value. Other benefits have been proposed to be gained from open-label extension studies. These include ongoing access to an effective but otherwise unobtainable medicine by the volunteers who participated in the phase III pivotal trials. However, there are unappreciated ethical issues about the appropriateness of enrolling patients whose response to previous treatment is uncertain, largely because treatment allocation in the preceding randomised, double-blind, controlled trial has not been revealed at the time of entry into the open-label extension study. Negative aspects of open-label extension studies revolve around their use as a marketing tool, as they build a market for the drug and generate pressure for subsidised access to the drug from consumers and their physicians. Consumers, institutions where these studies are conducted and research ethics committees need to be convinced of the motives, as well as the quality, of the open-label extension study and its execution before supporting such studies. Open-label extension studies do have a legitimate but limited place in the clinical development of new medicines. The negative perceptions about these studies have arisen because of perversion of acceptable rationales for this type of study and a failure to recognise (or disclose) the limitations resulting from the inherent weaknesses in their design. Increased human exposure to a new medicine under reasonably controlled circumstances to increase confidence in the safety of the medicine is an acceptable rationale for an open-label extension study, and a useful activity to increase the knowledge of the safety profile of a new medicine. However, this goal is increasingly being achieved by means other than open-label extension studies.