OBJECTIVE: Phosphorylcholine (PC) is one important epitope on oxidized low-density lipoprotein that may play an important role by contributing to the atherogenicity of oxidized low-density lipoprotein. IgM antibodies against PC (anti-PC) are present ubiquitously in the population as natural antibodies. We here determine the association between anti-PC and incidence of myocardial infarction (MI). METHODS: We studied 462 incident cases of first events of MI and 888 age-matched and sex-matched controls identified through 13 years of follow-up (1987-1999) of participants in a population-based study from northern Sweden. Relative risks (RRs) with 95% confidence intervals (CIs) of incident MI with adjustments for age, sex, geographical region, hypertension, diabetes, BMI, smoking habits, s-cholesterol and high-sensitivity C-reactive protein were determined. Anti-PC levels were measured by enzyme-linked immunoassay. RESULTS: Low anti-PC values were associated with increased risk of MI. Significant associations were found for values below 26.8 U/ml, corresponding to the lowest 25th percentile, and the highest association was seen below 16.9 U/ml. These results remained almost the same after adjustment for confounding factors (RR crude: 1.56, CI: 1.07-2.28 and RR adjusted: 1.69, CI: 1.09-2.54). CONCLUSION: Low levels of natural IgM anti-PC could play an important role as risk markers for development of MI. Adjustment for common confounders only marginally affected the RR, suggesting that the addition of IgM anti-PC add independent information to the more traditional risk factors.