Cholesterol-lowering drugs include three major pharmacological classes: a) fibrates, b) statines, HMG-CoA reductase inhibitors and c) cholestyramine. The late eighties were characterized by the introduction of HMG-CoA reductase inhibitors in therapeutics. For 12 months (1st January-31 December 1991), a prospective intensive program of pharmacovigilance investigated the occurrence of side effects among the three pharmacological classes of cholesterol-lowering drugs in a specialized unit for prevention of atherosclerosis and dyslipidemia. Among 3,506 out patients who received cholesterol-lowering drugs, 36 side effects were reported (i.e. 1 side effect for 98 out-patients). Most of the side effects were observed with statines (61%). The most frequently observed side effects were gastralgia (19.5%) observed with the three classes of drugs and hepatitis with HMG-CoA reductase inhibitors (8.5%) or fibrates (3%) whereas myopathy (12%) only occurred with statines. The other side effects were cutaneous (14%: eczema, skin rashes) or neuropsychiatric (11%: insomnia...) ones. This study emphasizes the low frequency of severe side effects (myopathy: 1 per 1,000 prescriptions, hepatitis: 1 per 1,000 prescriptions) with cholesterol-lowering drugs in current practice.