This study compared the efficacy of simvastatin 80 mg and atorvastatin 80 mg in the treatment of 26 patients with familial hypercholesterolaemia over 12 weeks using an open crossover trial format. Both, similarly, reduced LDL by 47 +/- 13% and 43 +/- 16% and median triglycerides by 22% and 27% respectively. However, atorvastatin reduced HDL by 2 +/- 24% compared with 8 +/- 30% increase with simvastatin (p = 0.05) affecting the LDL:HDL ratio achieved (4.478 +/- 1.56 vs 3.74 +/- 0.93, p = 0.001). Atorvastatin raised median fibrinogen by 15% compared with a non-significant 5% increase with simvastatin (p = 0.05). Simvastatin reduced lipoprotein (a) by a median 20% compared with baseline (p = 0.05) compared with 5% for atorvastatin. Side-effects, mostly gastrointestinal, were seen in four patients (16%) with atorvastatin compared with one case of myalgia with simvastatin (4%). We conclude both drugs are equally effective in LDL reduction but that simvastatin is superior in raising HDL and causes fewer side-effects. These results require confirmation in larger studies.