OBJECTIVE: To study the association between deficient mannose-binding lectin (MBL) genotypes and arterial thrombotic events in systemic lupus erythematosus (SLE). METHODS: Patients with SLE of Hispanic, African American, and Caucasian ethnicity from LUMINA (LUpus in MInorities, NAture versus nurture), a multiethnic, longitudinal study of outcome, were studied. Arterial thrombotic events (myocardial infarction, angina, coronary artery bypass graft surgery, stroke, claudication, gangrene, or tissue loss and/or peripheral arterial thrombosis) that occurred after diagnosis were recorded. Genotyping for MBL gene polymorphisms was performed and their distribution was compared between patients who did and did not have thrombotic events. RESULTS: There were 58 events (21 cardiovascular, 27 cerebrovascular, and 10 peripheral vascular) in 48 patients. Patients who had thrombotic events were older and were more likely to be smokers, to have more severe disease, and to have accrued more damage overall. Also, a larger proportion of these patients had C-reactive protein values in the highest quintile of distribution. No significant difference in arterial thrombotic events was found in patients homozygous for MBL-deficient alleles compared with others. Similar results were seen within ethnic groups. Caucasians who developed potential thrombotic events exhibited a higher frequency of MBL-deficient alleles, but the difference was not statistically significant for all events together or for cardiovascular and cerebrovascular events combined. However, when only the cerebrovascular events were considered, the difference became statistically significant. CONCLUSION: Age, smoking, and measures of activity and damage were associated with arterial thrombotic events in patients with SLE, but MBL-deficient genotypes were not, with cerebrovascular events in Caucasians being the exception. The relationship between MBL-variant alleles and arterial thrombotic events may exist only within select ethnic groups and event types.