Valsartan is a second class of angiotensin II receptor antagonist, indicated for the treatment of hypertension. The objective of the study was to monitor the safety of valsartan using the technique of prescription event monitoring (PEM), in patients who were prescribed this drug by general practitioners (GPs) in England. PEM is a noninterventional observation cohort technique. Exposure data were obtained from dispensed prescriptions issued between December 1996 and November 1998. Outcome data were obtained by sending questionnaires to prescribing GPs. The cohort comprised 12881 patients. Events most frequently reported as suspected adverse drug reactions were malaise/lassitude (37; 0.3% of total cohort), dizziness (19; 0.1%), and unspecified side effects (57; 0.4%). Events with the highest incidence density (ID(1) per 1000 patient-months of treatment) in the first month of treatment were malaise/lassitude (15.6), dizziness (11.8), and headache/migraine (10.9). Most frequent reasons for stopping valsartan were not effective (847; 6.6% of total cohort), malaise/lassitude (265; 21%), and dizziness (146; 1.1%). No unexpected serious adverse events were identified. Other events assessed as possibly related to valsartan use were impotence (37), dizziness (19), cough (9), facial oedema (5), hyperkalaemia (3), and angioneurotic oedema (1). There were four reports of exposure during pregnancy and 203 deaths (1.5%) in this cohort. In conclusion, this study monitored the safety profile of valsartan in a large cohort of patients in general practice in England. No untoward features other than dizziness were identified that were not mentioned in the prescribing guidance.