We report four cases of rhabdomyolysis and severe, disabling myopathy associated with HMG CoA reductase-inhibitor therapy. Patient developed symptoms following the addition of roxithromycin to combination lipid-lowering therapy with simvastatin and gemfibrozil. Patients 2 and 3 became symptomatic after developing acute on chronic renal impairment while taking simvastatin. The muscle biopsy of patient 3 revealed a necrotizing myopathy and the presence of inclusion bodies. Patient 4 developed symptoms within 4 weeks of starting cerivastatin monotherapy. The four cases illustrate the importance of considering the potential for drug interactions and making appropriate dosage adjustments for renal insufficiency in patients receiving HMG CoA reductase therapy.