Background: Epidemiological studies suggest an association between periodontal disease and coronary heart disease. It is possible that periodontal disease may contribute to plaque destabilization in patients with acute coronary syndrome. Aim: To assess the association between severity of periodontal disease, the number of acute plaques and extension of coronary artery disease in patients with acute coronary syndrome. Patients and methods: The severity of periodontal disease was assessed by skilled independent observers in patients with acute coronary syndrome subjected to coronary angiography. The periodental disease was classified as mild or severe. Acute plaques were defined on angiography as those with thrombi, ulcers or flow alterations. The extension of coronary disease was analyzed using the Sullivan score. Results: Forty three patients (35 males) aged 41 to 83 years, were studied. Mild and severe periodontal disease was present in 18 (42%) and 25 (58%) patients respectively. Seventy six percent of those with severe disease had two or more acute plaques, compared with 17% of those with mild disease (p<0.001). Median Sullivan score was 80.6 and 57.2 in patients with severe or mild periodontal disease respectively (p=0.001). Conclusions: Severe periodontal disease was associated with a higher number of acute coronary plasques and a higher extension of coronary artery disease, in patients with acute coronary syndromes (Rev Méd Chile 2005; 133: 183-9)