Patients with combined hyperlipidemia and low high-density lipoprotein (HDL) cholesterol levels may benefit from combination therapy with a statin and niacin; therefore, we assessed the efficacy and safety of rosuvastatin and extended-release (ER) niacin alone and in combination in 270 patients with this atherogenic dyslipidemia. Men and women > or =18 years with fasting total cholesterol levels > or =200 mg/dl, triglycerides 200 to 800 mg/dl, apolipoprotein B > or cf=110 mg/dl, and HDL cholesterol <45 mg/dl were randomized to 1 of 4 treatments in this 24-week, open-label, multicenter trial: rosuvastatin 10 to 40 mg; ER niacin 0.5 to 2 g; rosuvastatin 40 mg/ER niacin 0.5 to 1 g; or rosuvastatin 10 mg/ER niacin 0.5 to 2 g. Percent changes from baseline in low-density lipoprotein (LDL) cholesterol, non-HDL cholesterol, and other lipid measurements at week 24 were determined by analysis of variance, with statistical testing performed separately between the rosuvastatin monotherapy group and each remaining treatment group. Daily doses of rosuvastatin 40 mg reduced LDL and non-HDL cholesterol significantly more than either ER niacin 2 g or rosuvastatin 10 mg/ER niacin 2 g (-48% vs -0.1% and -36% for LDL cholesterol and -49% vs -11% and -38% for non-HDL cholesterol, respectively; p <0.01 for all comparisons); no additional reduction in LDL or non-HDL cholesterol was observed with the combination of rosuvastatin 40 mg/ER niacin 1.0 g (-42% and -47%; p = NS). Triglyceride reductions ranged from -21% (ER niacin monotherapy) to -39% (rosuvastatin 40 mg/ER niacin 1 g), but no observed differences were statistically significant. Compared with rosuvastatin alone, rosuvastatin 10 mg/ER niacin 2 g produced significantly greater increases in HDL cholesterol (11% vs 24%, p <0.001) and apolipoprotein A-I (5% vs 11%, p <0.017). Similar increases in HDL cholesterol and apolipoprotein A-I were noted between the monotherapy groups. Over 24 weeks, rosuvastatin alone was better tolerated than either ER niacin alone or the combinations of rosuvastatin and ER niacin.