BACKGROUND The aim of this study was to investigate whether an association could be demonstrated between coronary heart disease (CHD) and chronic periodontitis in a population of middle-aged males in Northern Ireland. METHODS A case-control design was used. Cases were men aged over 40 years with angiographically proven CHD. Controls were age-matched males, with no evidence of CHD, randomly drawn from the same locality as the cases. Each subject had a clinical periodontal examination and completed a detailed sociodemographic questionnaire. High sensitivity C-reactive protein (CRP) was measured in serum by immunoturbidimetry. RESULTS There were 92 cases (mean age 56.7 years; SD = 6.3) and 79 controls (mean age 58.2 years; SD = 6.7). The CHD cases had an average of three teeth less than the controls (P <0.0001). A higher proportion of sites examined in cases than controls had plaque (P = 0.004), bleeding on probing (P = 0.013), and probing depths of > or = 4 mm (P = 0.006) or > or = 6 mm (P = 0.03). Subjects with > or = 4 mm pocketing in more than 20% of their interproximal sites and those with deep pocketing (> or = 6 mm) were classified as having poor periodontal status. A total of 35 cases (38%), compared to only 13 controls (16%), had a poor periodontal status (P = 0.0017). Men with a poor periodontal condition had higher levels of CRP (median 2.19 mg/l) than those with good periodontal health (median 1.42 mg/l), P = 0.007. After adjusting for smoking, academic achievement, alcohol consumption, unemployment, ability to maintain body weight, regular exercise, ability to relax daily, having a hobby or pastime, plaque, and CRP, logistic regression analysis showed that poor periodontal status was significantly associated with CHD, with an adjusted odds ratio of 3.06 and 95% confidence intervals of 1.02 to 9.17, P = 0.046. CONCLUSIONS There was an association between coronary heart disease and poor periodontal status in the middle-aged males investigated. This association was independent of diabetes and all other cardiovascular risk factors investigated.