The National Heart, Lung, and Blood Institute, Bethesda, Md, sponsored national telephone surveys of practicing physicians and the adult public in 1983, 1986, and 1990 to assess attitudes and practices regarding high serum cholesterol levels. Each time, approximately 1600 physicians and 4000 adults were interviewed. Trends show continuing change in medical practice and public health behavior relating to serum cholesterol. In 1990, physicians reported treating serum cholesterol at considerably lower levels than in 1986 and 1983. The median range of serum cholesterol at which diet therapy was initiated was 5.17 to 5.66 mmol/L (200 to 219 mg/dL) in 1990, down from 6.21 to 6.70 mmol/L (240 to 259 mg/dL) in 1986 and 6.72 to 7.21 mmol/L (260 to 279 mg/dL) in 1983. The median ranges for initiating drug therapy were 6.21 to 6.70 mmol/L (240 to 259 mg/dL) in 1990, 7.76 to 8.25 mmol/L (300 to 319 mg/dL) in 1986, and 8.79 to 9.28 mmol/L (340 to 359 mg/dL) in 1983. The number of adults who reported having had their cholesterol level checked rose from 35% to 46% to 65% in 1983, 1986, and 1990, respectively. Between 1983 and 1990, the number of adults reporting a physician diagnosis of high serum cholesterol increased from 7% to 16%; the number reporting a prescribed cholesterol-lowering diet increased from 3% to 9%. Reports of self-initiated diet efforts reached a high of 19% in 1986 and decreased to 15% in 1990 compared with 1% in earlier years. In 1990, over 90% of physicians reported awareness and use of the recommendations from the Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults, and the public reported marked increases in awareness of dietary methods to lower serum cholesterol. These changes suggest educational gains; the data also suggest areas for continued cholesterol educational initiatives.