[영문]Objective: Clinicians are increasingly using handheld computers (HC) during patient care. We sought to assess the role of HC-based clinical reference software in medical practice by conducting a survey and assessing actual usage behavior. Design: During a 2-week period in February 2005, 3600 users of a HC-based clinical reference application were asked by e-mail to complete a survey and permit analysis of their usage patterns. The software includes a pharmacopeia, an infectious disease reference, a medical diagnostic and therapeutic reference and transmits medical alerts and other notifications during HC synchronizations. Software usage data were captured during HC synchronization for the 4 weeks prior to survey completion. Measurements: Survey responses and software usage data. Results: The survey response rate was 42% (n = 1501). Physicians reported using the clinical reference software for a mean of 4 years and 39% reported using the software during more than half of patient encounters. Physicians who synchronized their HC during the data collection period (n = 1249; 83%) used the pharmacopeia for unique drug lookups a mean of 6.3 times per day (SD 12.4). The majority of users (61%) believed that in the prior 4 weeks, use of the clinical reference prevented adverse drug events or medication errors 3 or more times. Physicians also believed that alerts and other notifications improved patient care if they were public health warnings (e.g. about influenza), new immunization guidelines or drug alert warnings (e.g. rofecoxib withdrawal). Conclusion: Current adopters of HC-based medical references use these tools frequently, and found them to improve patient care and be valuable in learning of recent alerts and warnings.