Objective: To investigate the trend of ambulatory calcium channel blockers (CCBs) utilization in Taiwan according to the national health insurance claims over an eight-year period. Special attention would be paid to the extent and situations of prescribing first-line (short-acting) CCBs on a PRN (pro re nata) order. Methods: The visit-based sampling claims datasets of ambulatory care visits from 1997 to 2004, offered by the National Health Insurance Research Database, were analyzed. The datasets represented 0.2% of total ambulatory care visits within the National Health Insurance in Taiwan. The utilization of CCBs was stratified by ingredient and formulation, and the prescriptions of CCBs on a PRN order by the patient's age, the prescribing physician's specialty, and the setting of health care facility. Results: During the study period, the CCBs had remained as the most popular antihypertensive agents in Taiwan. The number of defined daily doses (DDDs) of all CCBs per 1000 inhabitants per day increased from 15.3 in 1997 to 36.4 in 2004. The growth of CCBs was attributed to second- and third-generation CCBs, especially amlodipine. While the first-line CCBs, mainly short-acting nifedipine, became less popular with time (from 6.0 DDDs per 1000 inhabitants per day in 1997 to 3.5 in 2004), their PRN use did not have a diminishing trend. In 2004, the short-acting nifedipine on a PRN order still existed in 1.5% of prescriptions containing antihypertensive agents and 3.4% of prescriptions containing CCBs. More than one half of these PRN orders were prescribed by the internists and to the elderly patients; almost four-fifths of these PRN orders were prescribed during normal consultations. Conclusion: The physicians in Taiwan still had the habit of prescribing short-acting CCBs both on regular use and on PRN use. The reason for such practices and the impact on patients' health deserve attention.