The clinical efficacy and tolerability of simvastatin and fluvastatin were compared in 432 patients with primary hypercholesterolaemia in a multinational, randomised, double-blind trial. Following at least 10 weeks on a lipid-lowering diet, patients continuing to have a total cholesterol level ≥ 6.5 mmol/L and elevated low density lipoprotein (LDL) cholesterol levels received 6 weeks of once-daily treatment with either simvastatin 5mg (n = 109), simvastatin 10mg (n =110), fluvastatin 20mg (n = 105), or fluvastatin 40mg (n = 108). The relative potency rates of simvastatin to fluvastatin in reducing LDL and total cholesterol levels were estimated to be 7.60 and 7.65, respectively. Significantly greater mean reductions in LDL cholesterol levels were found at week 6 with simvastatin 10mg (30%) compared with either fluvastatin 20mg (22%; p < 0.001) or fluvastatin 40mg (26%; p = 0.03). Similarly, LDL cholesterol was lowered more in the simvastatin 5mg group (26%) than in the fluvastatin 20mg group (22%; p = 0.03). No significant difference was seen between simvastatin 5mg and fluvastatin 40mg. Plasma total cholesterol levels were also significantly lower with simvastatin 10mg compared with fluvastatin 20mg (23 vs 16%; p < 0.001) and fluvastatin 40mg (23 vs 19%; p = 0.02), and with simvastatin 5mg compared with fluvastatin 20mg (19 vs 16%; p = 0.01). Simvastatin 5mg and fluvastatin 40mg both lowered total cholesterol levels by 19%. The percentage of patients reaching National Cholesterol Education Program Adult Treatment Panel II (NCEP ATP II) target LDL cholesterol levels after 6 weeks’ treatment with simvastatin 5 or 10 mg/day or fluvastatin 20 or 40 mg/day was 24, 25, 12 and 21%, respectively. Tolerability profiles were generally similar, although significantly more gastrointestinal adverse events occurred in the fluvastatin-treated patients (23 vs 11%). In conclusion, simvastatin 10 mg/day is more effective in lowering total and LDL cholesterol levels than the maximum recommended dose of fluvastatin (40 mg/day), whereas simvastatin 5 mg/day and fluvastatin 40 mg/day showed similar efficacy.