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To review the current research of hidden populations of illicit drugs users using web-based methods and discuss major advantages and disadvantages.Systematic review of 16 databases, including PubMed, PsycINFO (EBSCOhost), CSA Sociological Abstracts, Expanded Academic ASAP and Google Scholar.Substances researched were most commonly ‘party/club drugs’ (such as ecstasy) and cannabis. All of the studies reviewed concluded that the internet is a useful tool for reaching hidden populations, but is likely to impose some bias in samples. Advantages include: access to previously under-researched target groups; speed; international applications; increased ease of data entry; and improved confidentiality for respondents. The major disadvantage is a lack of representativeness of samples.Internet research is successful at accessing hidden populations of illicit drugs users, when appropriately targeted and provides unprecedented opportunities for research across a wide range of topics within the addictions field. Findings are unlikely to be generalisable to the general public, but appropriate for describing target populations.