OBJECTIVES:   This study estimated market shares for six statins based on 1) the literature-determined lipid-lowering potential of the drugs, and 2) the distribution of U.S. adults depending on the amount of lipid-lowering they required.  Estimated market shares were compared with actual market shares. METHODS:   Two panels (1999-2000 and 2001-2002) from the National Health and Nutrition Examination Survey (NHANES) provided interview, demographic, and laboratory data for 3324 people > 20 years of age who were not taking a statin.  In accordance with the ATP III Guidelines, coronary heart disease (CHD) and CHD-risk-equivalent events including diabetes, other risk factors such as smoking and high blood pressure, and Framingham scores to obtain 10-year risk estimates were identified and calculated, respectively for each person, along with percentage LDL-C lowering required to reach his or her LDL-C goal.  Depending on the amount of lowering needed and on whether the individual had a liver condition, hence, enhanced risk of rhabdomyolysis, a particular statin or particular statins with equal probabilities were assigned to the individual; e.g., a person without a liver condition requiring 50% lowering of LDL-C would be assigned rosuvastatin or atorvastatin, each with probability = 0.5.     RESULTS:   Of 1643 men surveyed, 57.88% were in the lowest-risk group (0-1 risk factors); 14.36% were in the highest-risk group (CHD or CHD-risk-equivalent).  For the 1681 women, these percentages were 73.11% and 11.30%, respectively.  Of people needing a statin, 73.74% needed LDL-C lowering by < 25%; only 1.16% required LDL-C lowering of > 60%.  Therapeutic market shares were estimated at 20.11% (rosuvastatin); 18.94% (atorvastatin); 17.89% (simvastatin); 16.96% (lovastatin); 13.05% (fluvastatin); and 13.05% (pravastatin). CONCLUSIONS: Actual market shares are significantly different from market shares based on lipid-lowering considerations.  Explanations include direct-to-consumer advertising; varying pricing strategies; and clinical trials for additional indications and subpopulations conducted only by the market leaders.