BACKGROUND: Lipoprotein-associated phospholipase A2 (Lp-PLA2) levels are associated with coronary heart disease (CHD) in healthy individuals and in patients who have had ischemic events. METHODS AND RESULTS: The Long-term Intervention with Pravastatin in Ischemic Disease (LIPID) study randomized 9014 patients with cholesterol levels of 4.0 to 7.0 mmol/L to placebo or pravastatin 3 to 36 months after myocardial infarction or unstable angina and showed a reduction in CHD and total mortality. We assessed the value of baseline and change in Lp-PLA2 activity to predict outcomes over a 6-year follow-up, the effect of pravastatin on Lp-PLA2 levels, and whether pravastatin treatment effect was related to Lp-PLA2 activity change. Lp-PLA2 was measured at randomization and 1 year, and levels were grouped as quartiles. The prespecified end point was CHD death or nonfatal myocardial infarction. Baseline Lp-PLA2 activity was positively associated with CHD events (P < 0.001) but not after adjustment for 23 baseline factors (P = 0.66). In 6518 patients who were event free at 1 year, change in Lp-PLA2 was a significant independent predictor of subsequent CHD events after adjustment for these risk factors, including LDL cholesterol and LDL cholesterol changes (P < 0.001). Pravastatin reduced Lp-PLA2 by 16% compared with placebo (P < 0.001). After adjustment for Lp-PLA2 change, the pravastatin treatment effect was reduced from 23% to 10% (P = 0.26), with 59% of the treatment effect accounted for by changes in Lp-PLA2. Similar reductions in treatment effect were seen after adjustment for LDL cholesterol change. CONCLUSION: Reduction in Lp-PLA2 activity during the first year was a highly significant predictor of CHD events, independent of change in LDL cholesterol, and may account for over half of the benefits of pravastatin in the LIPID study.