Medline and reference lists of relevant articles were consulted.Papers were quality assessed by two reviewers: only those addressing passive ultrasonic irrigation (PUI) were included in the review.A qualitative synthesis describing the mechanism and effects of PUI is described.Fifty-four papers were included in the review and a qualitative summary of the findings presented.PUI appears to be a possible adjunctive treatment for cleaning the root canal system and may be more effective than syringe irrigation. More research is needed to clarify the underlying physical mechanisms through which PUI works.