Aims: To assess whether recurrence of acute coronary syndrome (ACS) can be linked to periodontitis in subjects followed over a 3 year period. Methods and results: Consecutive 163 hospital admitted subjects with ACS, and 158 medically healthy matched control subjects were followed through medical records review over 3 years. At baseline, subjects received medical and dental examinations. Periodontitis was defined as alveolar bone loss (ABL) > 2 S.D. above normal mean values. Subgingival bacterial samples were collected and processed by checkerboard DNA–DNA hybridization. ACS recurrence was found in 66/163 (40.5%) subjects, and a first ACS event in 7/158 (4.4%) control subjects. ABL was a risk marker of future ACS with OR: 3.6 (95%CI: 2.0-6.5, P < 0.001). Subject age was also an explanatory factor for a new ACS event (P < 0.001). Significantly higher subgingival bacterial counts for 20/37 species (i.e., Streptococcus anginosus, Streptococcus mitis, Tannerella forsythia) in ACS cases than in healthy controls. None of traditional serum markers (CRP, high and low density lipoprotein, cholesterol, triglycerides) were explanatory. Conclusions: Age, and periodontitis (ABL) are robust markers of risk for future ACS. Subgingival bacterial counts are elevated in subjects with ACS.