Controversy exists regarding the ethics of using placebo control groups in clinical trials when effective treatments exist. The debate was fuelled by the announcement of the fifth revision of the Declaration of Helsinki in 2000. This study reviews the history and scientific background surrounding the controversy and investigates the prevailing attitudes of Hong Kong researchers regarding this issue. The controversy has centred on several issues. The first involves the methodological superiority of placebo-controlled trials in discerning treatment effects. Secondly, it is unclear whether the treatment effects encompass absolute treatment effects (including placebo effects) or are confined to treatment-specific effects (excluding placebo effects). Thirdly, there are concerns that subjects in the placebo group could be exposed to a high risk for developing serious adverse events. Fourthly, it is unclear whether the standard of best available treatment should be local or international. Preliminary research findings suggest that the opinions of Hong Kong researchers are divided on the use of placebo control groups in clinical trials when effective treatment exists. Further research on the topic is therefore warranted, and training and consensus meeting may be necessary to minimise the confusion related to this issue.