OBJECTIVES: To evaluate the long-term clinical and cost outcomes of adding Niaspan® to statin treatment in patients with persistently low HDL-c on statin monotherapy. METHODS: Two models were developed to project long-term clinical and economic outcomes. The first model(second order Monte Carlo simulation) simulated the evolution of lipid levels with treatment and the second (Markov model) was designed to calculate the risk of coronary heart disease (CHD) events each subsequent year. Transition probabilities for CHD events were derived from the Framingham risk formulae. Baseline cohort characteristics and simvastatin treatment effects were taken from the 4S lipid triad sub-group. Patients with persistently low HDL-c (<1.03 mmol/L) on statin treatment received either add-on Niaspan® 1g to 2g daily or continued statin monotherapy. Niaspan® dosing followed maintenance dose recommendations and treatment effects were taken from several clinical trials (European SPC). Direct medical costs were accounted (cardiovascular complications and drug costs). Annual discount rates of 0% and 3.5% (Austria), 3% (Sweden and Norway) were applied to clinical outcomes and costs. RESULTS: 68.9% of patients were projected to have persistently low HDL-c levels after statin treatment. In these patients mean undiscounted life expectancies (LE) of 20.96 years and 20.46 years were projected for the Niaspan® and statin monotherapy arms respectively. Lifetime direct medical costs were higher by €8,079 in Austria, €4,723 in Sweden and €5,638 in Norway with addition of Niaspan®. Incremental cost-effectiveness ratios based on discounted LE were €16,306 (€17,635) per life year gained in Austria, €16,543 (€16,652) in Sweden and €19,748 (€21,194) in Norway for statin plus Niaspan® 1g (and 2g) versus statin monotherapy. CONCLUSIONS: In Austria, Sweden and Norway, raising HDL-c with the addition of Niaspan® to statin therapy was projected to be cost-effective compared to statin monotherapy in patients with dyslipidemia and persistently low HDL-c.