Illegible or invalid hand-written prescriptions can result in avoidable medical errors. Computer-based prescribing can mitigate the problem. An observational study was performed to examine the effect of wireless handheld computers (handhelds) on voluntary utilization of computerized prescribing within an Emergency Department. Handhelds with prescription-writing software were provided to physicians and the numbers of hand-written and computer-generated prescriptions were compared before and after the introduction of the handhelds. The resulting increase in computer-based prescribing was statistically significant and was observed largely among physicians who already used desktop computers for prescribing. The study concluded that handhelds increased voluntary utilization of computerized prescribing, but that the physicians most likely to use handhelds were those who already used desktop-based prescribing.