OBJECTIVE The aim of this study was to assess systematically the adjunctive effect of both flossing and toothbrushing versus toothbrushing alone on plaque and gingivitis. METHODS The MEDLINE and Cochrane Central register of Controlled Trials (CENTRAL) databases were searched through December 2007 to identify appropriate studies. The variables of plaque and gingivitis were selected as outcomes. RESULTS Independent screening of titles and abstracts of 1166 MEDLINE-Pubmed and 187 Cochrane papers resulted in 11 publications that met the eligibility criteria. Mean values and SD were collected by data extraction. Descriptive comparisons are presented for brushing alone or brushing and flossing. A greater part of the studies did not show a benefit for floss on plaque and clinical parameters of gingivitis. A meta-analysis was performed for the plaque index and gingival index. CONCLUSIONS The dental professional should determine, on an individual patient basis, whether high-quality flossing is an achievable goal. In light of the results of this comprehensive literature search and critical analysis, it is concluded that a routine instruction to use floss is not supported by scientific evidence.