Partial ileal bypass (PIB) was performed in 8 young adults (5 males and 3 females, mean age 37 +/- 5 years) with a history of vascular surgery (aorto-coronary bypass, ACB, n = 6; stroke, n = 2), presenting with hyperlipidemia (II B: n = 7; IIA: n = 1). None of the patients had diabetes, 2 had mild hypertension, and all were cigarette smokers. Hypolipidemic drugs were discontinued prior to PIB. Following bypass surgery, patients received vitamin B12 injections twice monthly. Total plasma cholesterol (TPC) and total plasma triglycerides (TPT) were assayed at 3 months and 1 year after surgery. The mean follow-up period was 84 months. Mean TPC level was significantly lower (3.96 +/- 0.57 preoperatively vs 2.19 +/- 0.79 (p less than 0.001) and 2.54 +/- 0.76 (p less than 0.01) 3 months and 1 year postsurgery, respectively. Mean TPT level was significantly lower 3 months after the intervention (4.85 +/- 2.37 vs 2.33 +/- 0.62, p. less than 0.02), but not after one year. Similar trends were observed throughout the follow-up period. One of the ACB patients died of drowing, while three others had recurring angina pectoris symptoms. Coronary angiography showed that, despite low TPC levels, coronary artery disease had extended either to other vessels not included in the former bypass, or beyond the anastomoses. Patients with a history of stroke were asymptomatic. PIB is effective in normalizing TPC. Nonetheless, this isolated procedure is insufficient to prevent the evolution of multifactorial atherosclerosis.