Introduction Hypnosis is one of the oldest forms of complementary and alternative medicine as well as a psychological intervention. Derived from its Greek origin, the term was once mythically associated with sleep. Because hypnosis is commonly more related to relaxation and imagery under suggestion, the approach may be helpful to improve insomnia by reducing hyperarousal. This presentation discusses its components, effectiveness and potential for treating insomnia. Materials and methods Review of literature on the nature, characteristics and components and measurements of hypnosis and critical appraisal of 6 randomized controlled trials (RCTs) from 1970s to 2000s identified from keywords search in databases on the components, treatment regime of hypnosis as well as study design, methodology and limitations. Results Despite lacking a unique definition, some characteristics of hypnosis such as lack of voluntary initiation and a fading of generalized reality orientation are recognized. Hypnotic responses are often assessed by behavioural scales or self-reported inventories. Another practice to operationalize hypnosis is the use of hypnotizability scales to measure the extent a subject responds to standardized suggestions presented after a standardized hypnotic induction procedure. The appraisal of the studies found that methodological quality of the included studies was low. Limitations include imprecise enrollment criteria and diagnostic procedure, unclear randomization and allocation concealment methods, inadequate outcome assessment and descriptions of withdrawal and dropouts, and lack of adverse event monitoring. None of the reviewed RCTs have assessed the hypnotic responses or the success of blinding of participants, though some argue that blinding is not possible in hypnosis. Despite low quality, most RCTs reported that a significant improvement in sleep parameters could be achieved in 4 weekly sessions or less and no adverse events were reported. Conclusion Although the overall results suggested that hypnosis treatment was safe and efficacious for treating insomnia, due to the methodological limitations, the generalizabilty of the positive findings remained questionable. Future studies with larger sample size, better study design and methodological quality are needed to ascertain the efficacy of hypnosis for insomnia. Acknowledgements This presentation is part of my research project for PhD candidature at the Department of Psychiatry, University of Hong Kong.