An observational study was performed to compare five compounds as initial therapy to evaluate the persistence with antihypertensive treatment and drug cost. Over a 1-year follow-up period on the entire population (approximately 360,000 residents) of the Ravenna Local Health Unit. The presence of five major antihypertensive agents between January 1st, and December 31st, 1997 was investigated. There were 4614 patients enrolled. The annual average cost of treatment ranged between euro 44.27 (95% confidence interval, 38.18-52.06) for patients started on atenolol to euro175.65 (150.37-205.10) for those started on losartan. Patients who began losartan showed a higher posterior probability of an effective antihypertensive treatment. On average, these patients turned to produce cost-effective treatment with an average probability of 0.70.