PubMed/Medline, Embase, Cochrane Central Register of Controlled Clinical trials (CENTRAL), Web of Knowledge, SCOPUS, Google Scholar and LILACS databases.Clinical prospective and retrospective studies of orthodontic treatment with clear aligners on patients over the age of 15 that included clear descriptions of the materials and applied technique were included. Selection was undertaken independently by two reviewers.Two reviewers extracted data independently with study quality being assessed using the grading system described by the Swedish Council on Technology Assessment in Health Care (SBU). A narrative summary of the findings was presented.Eleven studies involving a total of 480 patients were included consisting of two randomised controlled trials, five prospective studies and four retrospective studies. Six studies were considered to be of moderate quality, the remainder of limited quality.Most of the studies presented with methodological problems: small sample size, bias and confounding variables, lack of method error analysis, blinding in measurements, and deficient or missing statistical methods. The quality level of the studies was not sufficient to draw any evidence-based conclusions.