We investigated for the first time in the Moroccan population the relationship between lipoprotein particles and the progression of coronary atherosclerosis. Plasma lipid variables, including total cholesterol, triglycerides, high-density lipoprotein-cholesterol, low-density lipoprotein-cholesterol, apolipoproteins AI and B, Lp AI, Lp AI: AII, and Lp(a) were measured in 40 Moroccan adults who suffered a verified myocardial infarction before the age of 50 years. The results were compared with a healthy control group. Plasma total cholesterol, triglyceride, and Lp AI: AII levels of patients did not differ significantly from control subjects. Patients had lower plasma high-density lipoprotein-cholesterol (P < 0.05), apo AI (P < 0.05), and Lp AI (P < 0.001) than control subjects, suggesting that the cholesterol reverse transport system is altered in patients with previous myocardial infarction. However, patients had higher plasma low-density lipoprotein-cholesterol (P < 0.001), apo B (P < 0.001), and Lp(a) (P < 0.001). In all patients the best predictor of cardiovascular risk was the independent risk factor Lp(a) plasma level, and the Lp AI plasma level. In this study, the increased coronary atherosclerosis risk with elevated plasma levels of apo B and Lp(a), and with reduced Lp AI, was substantially modified by smoking habits, but not by family history of myocardial infarction.