BACKGROUND: High intakes of saturated fat have been associated with cardiovascular disease, and milk fat is rich in saturated fat. OBJECTIVE: The objective of this study was to investigate the association between the serum milk fat biomarkers pentadecanoic acid (15:0), heptadecanoic acid (17:0), and their sum (15:0+17:0) and a first myocardial infarction (MI). DESIGN: The study design was a prospective case-control study nested within a large population-based cohort in Sweden. Included in the study were 444 cases (307 men) and 556 controls (308 men) matched on sex, age, date of examination, and geographic region. Clinical, anthropometric, biomarker fatty acid, physical activity, and dietary data were collected. The odds of a first MI were investigated by using conditional logistic regression. RESULTS: In women, proportions of milk fat biomarkers in plasma phospholipids were significantly higher (P