INTRODUCTION: The development of tools to meet the information needs of clinicians requires an understanding of the clinician and the context in which clinical decisions are being made. METHODS: We conducted an observational study of clinicians' information needs via think-aloud protocols during which we observed physicians and nurses as they used the clinical information system. Protocol analysis was then used to identify the information needs events, the types of questions that were asked, the method of meeting that need, the success or failure of meeting the specific information need, and the context in which it arose. RESULTS: Results indicated that a) unmet information needs occur frequently and that b) the predominant feature of these unmet needs is that they are patient-related or domain-specific. Two categories of context: laboratory and medical communication accounted for more than half of the events.