Between December 1989 and December 1992, the Netherlands Centre for Monitoring of Adverse Reactions to Drugs received 142 reports of suspected adverse reactions to simvastatin or pravastatin. In 108 of these, the causal relationship was considered 'definite', 'probable' or 'possible'. The patients were 49 males and 59 females with mean age of 55 and 59 years respectively, with a total of 157 reported suspected adverse reactions. The most important effects reported comprised muscle and vision disorders, interactions with coumarins, liver damage and psychic effects. With the exception of rhabdomyolysis and symptomatic liver damage the adverse effects of cholesterol synthesis inhibitors appear to be fairly innocuous. It should be emphasized, however, that too little is yet known of the psychic and long-term effects for an adequate judgment of the benefit-risk ratio of these agents.