Background. The authors conducted a systematic review of the literature to determine the treatment effects of the Invasalign orthodontic system (Align Technology, Santa Clara, Calif). Types of studies reviewed. The authors reviewedclinical trials that assessed Invisalign's treatment effects in nongrowing patients. They did not consider trials involving surgical or other simultaneous fixed or removable orthodontic treatment interventions. Results. The authors searched electronic databases (PubMed, MEDLINE, MEDLINE In-Process & Other Non-Indexed Citations Evidence Based Medicine Reviews, EMBASE Excerpta medica, Thomsen's ISI web of science and LILACS)with the help of a senior health sciences librarian. They used "Invisalign" as the sole search term, and 22 documents appeared in the combined search. Thereafter, they used"clinical trials" "humans" and "Invisalign treatment effects" as abstract selection criteria. Only two published articles met these inlclusion criteria, though after reading the actual articles, the authors determined that they did not adequately evaluate Invisalign treatment effects. Both articles identified methodological issues. Clinical Implications. The inadequately designed studies the authors found represented only a lower level of evidence (level II). Therefore, the authors found that no strong conclusions could be made regarding the treatment effects of Invisalign appliances. Future prospective randomized clinical trials are required to support, with sound scientific evidence, the claims about Invisalign's treatment effects. Clinicians will have to rely on theirInvisalign clinical experience, the opiniomns of experts and the limited published evidence when using Invisalign appliances.