The prevalence and clinical aspects of high-HDL-cholesterolemia were investigated in 2000 patients (1215 males and 785 females) aged 14-88 years in our medical outpatient department. The incidence of high-HDL-cholesterolemia was 7% (greater than 1.68 mmol/l) in males and 9.9% (greater than 1.94 mmol/l) in females and was associated in 80% of cases with a normal lipid profile according to the Fredrickson classification. Compared with patients with low-HDL-cholesterolemia, high-HDL-cholesterolemia distinguished by a lower incidence of obesity, of hyperlipidemia, of diabetes and of cigarette smoking. In contrast, daily alcohol intake was significantly higher. Fewer patients had a history of ischemic cardiovascular events. High-HDL-cholesterolemia appears to arise from both environmental and genetic factors.