Objective Some researchers claim that the quality of informed consent of clinical research participants in developing countries is worse than in developed countries. To evaluate this assumption, we reviewed the available data on the quality of consent in both settings. Methods We conducted a comprehensive PubMed search, examined bibliographies and literature reviews, and consulted with international experts on informed consent in order to identify studies published from 1966 to 2010 that used quantitative methods, surveyed participants or parents of paediatric participants (...) in actual trials, assessed comprehension and/or voluntariness, and did not involve testing particular consent interventions. Forty-seven studies met these criteria. We compared data about participant comprehension and voluntariness. The paucity of data and variation in study methodology limit comparison and preclude statistical aggregation of the data. Results and Discussion This review shows that the assertion that informed consent is worse in developing countries than in developed countries is a simplification of a complex picture. Despite the limitations of comparison, the data suggest that: (1) comprehension of study information varies among participants in both developed and developing countries, and comprehension of randomisation and placebo controlled designs is poorer than comprehension of other aspects of trials in both settings; and (2) participants in developing countries appear to be less likely than those in developed countries to say they can refuse participation in or withdraw from a trial, and are more likely to worry about the consequences of refusal or withdrawal. (shrink)