This report describes the design and baseline results of the Kyushu Lipid Intervention Study (KLIS). The study aims to test the hypothesis that the long term reduction of serum total cholesterol by pravastatin will lead to a decrease in coronary heart disease (CHD) events. The trial was designed to include a random 6,000 male patients aged 45-74 years with serum total cholesterol of 220 mg/dl (5.69 mmol/l) or greater and without a history of myocardial infarction, coronary surgery or angioplasty, to undertake either pravastatin or conventional treatment (including hypolipidemic drugs other than HMG CoA reductase inhibitors, probucol and bezafibrate), and to follow up each patient for 5 years. Primary endpoints are fatal and nonfatal myocardial infarction, coronary bypass surgery and angioplasty, cardiac death, and sudden and unexpected death. During the period from May 1990 to September 1993, a total of 5,640 male patients aged 45-74 were recruited by 902 participating physicians throughout Kyushu. Randomization was, however, neglected by study physicians; the numbers of patients enrolled were 3,061 in the pravastatin group and 2,579 in the conventional treatment group. Patients allocated to the pravastatin treatment were generally unfavorable regarding coronary risk factors. Baseline mean levels of serum total cholesterol were 259 mg/dl (6.70 mmol/l) in the pravastatin group and 246 mg/dl (6.36 mmol/l) in the conventional treatment group (p <0.001). Although the trial was regarded as a prospective observational study, the KLIS provides valuable quantitative data regarding cholesterol lowering and reduction in CHD events as well as safety data of the long-term use of a statin in Japanese men with hypercholesterolemia.