OBJECTIVES: The ALLHAT findings (December 2002) recommended thiazide-type diuretics for first-step therapy in uncomplicated hypertensive patients, rather than either calcium channel blockers (CCBs) or angiotensin-converting enzyme (ACE) inhibitors. The objective of this study was to examine prescribing patterns for antihypertensive agents in Region Emilia Romagna (RER), Italy, following the ALLHAT publication. METHODS: We studied automated pharmacy claims of approximately 4 million RER residents between January 1, 2000 and December 31, 2003. We computed the monthly relative percentage of filled prescriptions for six antihypertensive classes: thiazide-type diuretics, ACE inhibitors or angiotensin receptor blockers (ARBs), CCBs, beta-blockers, alpha-blockers, and other-type antihypertensive diuretics. A stepwise auto-regressive forecasting model was used for time series analysis. To assess the impact of the ALLHAT guidelines on use of each antihypertensive class, predicted relative percentages and 95% confidence intervals were calculated for the 12 months of 2003. RESULTS: During the study period, ACE inhibitors/ARBs and CCBs had the largest relative percentages (approximately 40% and 30%, respectively), while the relative percentages for beta-blockers and thiazide-type diuretics were roughly 10% and 1%, respectively. Use of thiazide-type diuretics and ACE inhibitors/ARBs showed an overall upward trend, which was not statistically associated with the ALLHAT publication. The relative percentage of CCBs diminished over time and was statistically significant compared with that predicted by the time-series model in the last four months of 2003 (p<.05). The percentage of beta-blockers was stable during the study period, although statistically significantly higher in the last 7 months of 2003 compared with the predicted values (p<.05). Use of alpha-blockers and other-type antihypertensive diuretics was steady over time. CONCLUSIONS: The well-publicized ALLHAT findings had a limited impact on the prescribing patters of antihypertensive drugs in Italy. Further research should investigate why physicians appeared to be unresponsive to the new clinical evidence.