Objective Poor oral health is common in dementia, but findings of epidemiological studies have been inconsistent. This meta-analysis examined oral health in patients with dementia diagnosed according to standardized diagnostic criteria. Methods Six international databases (PubMed, EMBASE, PsycINFO, Medline, Cochrane Library, and Web of Science) were searched from their commencement date until 8 November 2018. Oral health was measured by the Remaining Teeth (RT) and Decayed, Missing, and Filled Teeth (DMFT) Index. The mean differences (MD) and 95% confidence intervals (CI) of DMFT Index total and component scores were calculated using a random-effect model. Results Twenty-four studies were included for analyses. The pooled DMFT Index was 23.48 (95% CI: 22.34, 24.62), while the pooled score for each component was 2.38 (95% CI: 1.56, 3.20) in decayed teeth (DT), 18.39 (95% CI: 15.92, 20.87) in missing teeth (MT), 2.29 (95% CI: 0.62, 3.95) in filled teeth (FT), and 11.59 (95% CI: 9.14, 14.05) in RT. Compared to controls, people with dementia had significantly a higher DMFT Index total score (MD = 3.80, 95% CI: 2.21, 5.39, p < 0.00,001), and significantly lower number of RT (MD = -3.15, 95% CI: -4.23, -2.06, p < 0.00,001). Subgroup analyses revealed that higher DMFT Index score was significantly associated with year of survey (>2010), study design (case-control study), percentage of females (<= 54.3), and the Mini Mental State Examination score (<= 18.2). Higher MT score was significantly associated with study design (cross-sectional study), and lower FT score was significantly associated with year of survey (>2010). Conclusions Oral health was significantly poorer in people with dementia compared with controls. Regular screening and effective treatment should be implemented for this population.