The objective of this systematic review was to evaluate analytical studies on periodontal disease as a possible risk factor for adverse pregnancy outcomes. A literature search of the MEDLINE, SciELO, and LILACS bibliographic databases and CAPES thesis database was conducted up to December 2005, covering epidemiological studies of periodontal disease and adverse pregnancy outcomes. Of the 964 papers identified, 36 analytical studies met the inclusion criteria. Twenty-six epidemiological studies reported associations between periodontal disease and adverse pregnancy outcomes. There was a clear heterogeneity between studies concerning measurement of periodontal disease and selection of type of adverse pregnancy outcome. Therefore no meta-analysis was performed. Most studies did not control for confounders, thus raising serious doubts about their conclusions. The methodological limitations of most studies did not allow conclusions concerning the effects of periodontal disease on adverse pregnancy outcomes. Larger and methodologically rigorous analytical studies using reliable outcomes and exposure measures are recommended.